ESQL - docs for to_date_nanos (#120124)

I forgot to link the ToDateNanos docs when I merged that function.
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Co-authored-by: elasticsearchmachine <[email protected]>
 Conflicts:
	docs/reference/esql/functions/description/to_date_nanos.asciidoc
	docs/reference/esql/functions/kibana/definition/to_date_nanos.json
	docs/reference/esql/functions/kibana/docs/to_date_nanos.md
	docs/reference/esql/functions/layout/to_date_nanos.asciidoc

Author: not-napoleon