Add ESQL MONTH_NAME function (elastic#132968)

Author: romulets

docs/reference/query-languages/esql/_snippets/functions/description/month_name.md

@@ -4,4 +4,5 @@
 * [`DATE_PARSE`](../../functions-operators/date-time-functions.md#esql-date_parse)
 * [`DATE_TRUNC`](../../functions-operators/date-time-functions.md#esql-date_trunc)
 * [`DAY_NAME`](../../functions-operators/date-time-functions.md#esql-day_name)
+* [`MONTH_NAME`](../../functions-operators/date-time-functions.md#esql-month_name)
 * [`NOW`](../../functions-operators/date-time-functions.md#esql-now)

docs/reference/query-languages/esql/_snippets/functions/examples/month_name.md

@@ -31,6 +31,9 @@ mapped_pages:
 :::{include} ../_snippets/functions/layout/day_name.md
 :::
 
+:::{include} ../_snippets/functions/layout/month_name.md
+:::
+
 :::{include} ../_snippets/functions/layout/now.md
 :::