ESQL: Add multi_match function

[ioanatia]

We want to add another search function, this time for the multi_match query.

Example:

FROM search-movies
| WHERE multi_match([title, plot, summary], "harry potter", { "type": "cross_fields" })

The multi_match function should accept the same options as the multi_match query.

[elasticsearchmachine]

Pinging @elastic/es-search-relevance (Team:Search Relevance)

[elasticsearchmachine]

Pinging @elastic/kibana-esql (ES|QL-ui)

[carlosdelest]

A good PR to learn about how to add a full text search function is the term query PR

[ioanatia]

As a follow up refactor, once we have the multi_match function we should be looking at removing MultiMatchQueryPredicate. I am not attempting to remove it before since I think that might conflict a bit with the changes for multi_match.