Description

As the ESQL grammar evolves, we need to establish some guidelines around the grammar and what are the expectations for clients using an old version or a a new version against a cluster that hasn't been fully upgraded.

Break-down of tasks

• Enable and validate version parameter for _query endpoint ESQL: Introduce language versioning to REST API #106824
• Update docs ESQL: Add version to docs #107225 ESQL: More explanation for version #107363
• Update REST spec not necessary since we only change the body of the REST request, which is not covered by the REST spec.
• Update elasticsearch-specification Add esql version elasticsearch-specification#2512
• Update integration tests and make version a required parameter after some grace period. ESQL: Default ESQL version on old clients #107438 ESQL: Send language version in spec tests #107268 ESQL: Make esql version required in REST requests #107433
• Update rally benchmarks Send version with esql rally#1841 (comment)