[DOCS] Changes wording to move away from data frame terminology in Stack Docs

[szabosteve]

Related to #518

This PR changes the wording of the data frame analytics limitation- and the evaluate data frame analytics pieces to move away from the data frame terminology.

Other occurrences of the data frame or data frames expressions were necessary to leave in the text (limitation piece & index).

List of occurrences:

Istvan-MacBook-Pro:stack-docs[master]$ find docs -name '*.asciidoc' | xargs egrep 'data frame'
Istvan-MacBook-Pro:stack-docs[master]$ find docs -name '*.asciidoc' | xargs egrep 'dataframe'
docs/en/stack/redirects.asciidoc:* <<dataframe-limitations>>
docs/en/stack/ml/df-analytics/ecommerce-outliers.asciidoc:For more details about creating {transforms}, see <<ecommerce-dataframes>>.
docs/en/stack/ml/df-analytics/dfanalytics-limitations.asciidoc:=== Deleting a {dfanalytics-job} does not delete the {dataframe} destination index
docs/en/stack/ml/df-analytics/dfanalytics-limitations.asciidoc:the {dataframe} destination index. That index must be deleted separately.
docs/en/stack/ml/df-analytics/dfanalytics-limitations.asciidoc:[[dfa-dataframe-size-limitations]]
docs/en/stack/ml/df-analytics/dfanalytics-limitations.asciidoc:=== {dataframe-cap} memory limitation
docs/en/stack/ml/df-analytics/dfanalytics-limitations.asciidoc:{dfanalytics-cap} can analyze {dataframes} that fit into the memory limit 
docs/en/stack/ml/df-analytics/index.asciidoc:{stack-ov}/ml-dataframes.html[{dataframe}]. 
docs/en/stack/ml/df-analytics/index.asciidoc:{dataframes} which can be used as the source for {dfanalytics}.
docs/en/stack/ml/df-analytics/evaluatedf-api.asciidoc:{dataframe} row with the ground truth. For example, in case of {oldetection}, 
Istvan-MacBook-Pro:stack-docs[master]$ 

[lcawl]

LGTM!

[szabosteve]

Backported to 7.x, 7.4, and 7.3.