Add galah_identify

[daxkellie]

To be consistent that functions prefixed by search_ are used for information lookup, whereas function prefixed by galah_ are used for filtering queries, making a galah_ function for taxonomic filtering will be more intuitive and consistent.

galah_identify will act as a filtering function within data queries, e.g., :

galah_call() %>%
  galah_identify("reptilia") %>%
  atlas_counts()

Then search_taxa will then be simplified to be a taxa lookup function that cannot be used within a galah_call() piped query

[daxkellie]

Addressed in previous commits:
2850a45
9b98c00
0d5b14d