SPARKNLP-786 Add support for non-schema NER tags

[maziyarpanahi]

This PR adds support for NER tags without any schema to be detected correctly in NerConverter annotator.

Currently, if the NER labels/tags generated by NerDLModel or any XXXForTokenClassification annotators have no schema (IO/IOB/IOB2/etc.) the NerConverter has some difficulties to extract the tag in its metadata.

IOB/IOB2 -> I-PER / B-PER
without Schema -> PER

+----------------------------------------------------------------------------------------------+
|result                                                                                        |
+----------------------------------------------------------------------------------------------+
|[PER, PER, O, O, O, LOC, O, O, O, LOC, O, O, O, O, PER, O, O, O, O, LOC]                      |
|[ORG, PER, O, O, O, O, O, O, O]                                                               |
|[ORG, O, ORG, O, O, O, ORG, ORG, O]                                                           |
|[LOC, O]                                                                                      |
|[PER, PER, O, O, O, O, O, O, O, O, O, LOC, O, LOC, O, O, O, O, O, O, O, O, O, O, O, O, O, LOC]|
|[LOC, O, O, O, O, LOC, LOC, O]                                                                |
|[PER, PER, O, O, O, LOC]                                                                      |
|[O, O, O, O, O, MISC, O, O, MISC, O, O, O, O, O, O, O, O, O, O, O, O, O, O]                   |
+----------------------------------------------------------------------------------------------+

+-------------------------------------------+
|result                                     |
+-------------------------------------------+
|[John Lenon, London, Paris, Sarah, London] |
|[Rare Hendrix]                             |
|[EU, German, British lamb]                 |
|[TORONTO]                                  |
|[Barack Obama, Honolulu, Hawaï, États-Unis]|
|[Paris, la France]                         |
|[george washington, washington]            |
|[Camembert, Français]                      |
+-------------------------------------------+

+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
|metadata                                                                                                                                                                                                                                                                                                                                        |
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
|[{entity -> R, sentence -> 0, chunk -> 0, confidence -> 0.9936409}, {entity -> C, sentence -> 0, chunk -> 1, confidence -> 0.9953128}, {entity -> C, sentence -> 0, chunk -> 2, confidence -> 0.99524385}, {entity -> R, sentence -> 0, chunk -> 3, confidence -> 0.790784}, {entity -> C, sentence -> 0, chunk -> 4, confidence -> 0.99527025}]|
|[{entity -> G, sentence -> 0, chunk -> 0, confidence -> 0.6287162}]                                                                                                                                                                                                                                                                             |
|[{entity -> G, sentence -> 0, chunk -> 0, confidence -> 0.9442431}, {entity -> G, sentence -> 0, chunk -> 1, confidence -> 0.71734494}, {entity -> G, sentence -> 0, chunk -> 2, confidence -> 0.8528497}]                                                                                                                                      |
|[{entity -> C, sentence -> 0, chunk -> 0, confidence -> 0.98190045}]                                                                                                                                                                                                                                                                            |
|[{entity -> R, sentence -> 0, chunk -> 0, confidence -> 0.99367046}, {entity -> C, sentence -> 0, chunk -> 1, confidence -> 0.995496}, {entity -> C, sentence -> 0, chunk -> 2, confidence -> 0.9955146}, {entity -> C, sentence -> 0, chunk -> 3, confidence -> 0.9870782}]                                                                    |
|[{entity -> C, sentence -> 0, chunk -> 0, confidence -> 0.99531066}, {entity -> C, sentence -> 0, chunk -> 1, confidence -> 0.8560585}]                                                                                                                                                                                                         |
|[{entity -> R, sentence -> 0, chunk -> 0, confidence -> 0.9946363}, {entity -> C, sentence -> 0, chunk -> 1, confidence -> 0.9790525}]                                                                                                                                                                                                          |
|[{entity -> SC, sentence -> 0, chunk -> 0, confidence -> 0.98350376}, {entity -> SC, sentence -> 0, chunk -> 1, confidence -> 0.9772832}]                                                                                                                                                                                                       |
+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

The issue here is the G or SC which is a partial extraction of the tags without any schema. This PR adds a support to extract non-schema NER tags in metadata.