ESQL: Add support for Full Text Functions for Lookup Join

[julian-elastic]

• Added Full Text Functions Support in Lookup Join Expressions: Extended lookup join functionality to support full-text functions like MATCH() as part of join conditions, enabling text search capabilities within lookup operations.
• Enhanced Lucene Pushable Filters Support. Implemented support for any Lucene pushable filters that contain only fields from the right side of the lookup join, allowing for more complex filtering conditions. At least one condition relating the left and right side of the Lookup Join is still required.

Full text function

FROM left_table
| LOOKUP JOIN right_table ON left_id == right_id AND MATCH(right_field, "search_term")

OR of Lucene pushable filters on fields from the lookup index

FROM left_table
| LOOKUP JOIN right_table ON left_id == right_id AND (right_field like "*pattern" OR right_value > 1000)

OR and NOT of Lucene pushable filters on fields from the lookup index

FROM left_table
| LOOKUP JOIN right_table ON (MATCH(right_field, "search_term") AND right_value < 5000 OR NOT (right_field != "exclude1" AND right_field != "exclude2")) AND left_id == right_id

[elasticsearchmachine]

Hi @julian-elastic, I've created a changelog YAML for you.

[elasticsearchmachine]

Pinging @elastic/es-analytical-engine (Team:Analytics)

[carlosdelest]

LGTM from the full text functions perspective 👍 :

• Changes imply adding checks for lookup join conditions
• IT tests have been updated with relevant tests