[DOCS] SQL: Document null handling for functions

[jrodewig]

Closes #74193.

Previews

• Aggregate functions: https://elasticsearch_74444.docs-preview.app.elstc.co/guide/en/elasticsearch/reference/master/sql-functions-aggs.html
• Date/time functions: https://elasticsearch_74444.docs-preview.app.elstc.co/guide/en/elasticsearch/reference/master/sql-functions-datetime.html
• Geo functions: https://elasticsearch_74444.docs-preview.app.elstc.co/guide/en/elasticsearch/reference/master/sql-functions-geo.html
• Grouping functions: https://elasticsearch_74444.docs-preview.app.elstc.co/guide/en/elasticsearch/reference/master/sql-functions-grouping.html
• Math functions: https://elasticsearch_74444.docs-preview.app.elstc.co/guide/en/elasticsearch/reference/master/sql-functions-math.html
• Type conversion functions: https://elasticsearch_74444.docs-preview.app.elstc.co/guide/en/elasticsearch/reference/master/sql-functions-type-conversion.html

[elasticmachine]

Pinging @elastic/es-docs (Team:Docs)

[elasticmachine]

Pinging @elastic/es-ql (Team:QL)

[matriv]

Regarding the date-time functions we also mention this in the description, for example: https://github.com/elastic/elasticsearch/pull/74444/files#diff-34118c3c46bec17c634fc5efa70c4ff0ff62e198a106564f175d1dae4d754447R705
(if one of the arguments is null then a null is returned)

Should we keep this as well ?

[jrodewig]

Thanks for catching that @matriv. I've removed those statements from the date/time function docs with 1f9209a.

[matriv]

LGTM. Thank you!

[jrodewig]

Thanks @matriv!