ESQL: Introduce Cross Cluster Query (CCQ) support

[costin]

Support ESQL queries to query both local and remote cluster indices.

Foundation

• ESQL now supports CCQ: Support cross clusters query in ESQL #101640

Enrich

• Resolve policies across clusters: Prepare enrich plan to support multi clusters #104355
• Support any mode: Support enrich ANY mode in cross clusters query #104840
• Support coordinator mode: Support enrich coordinator mode #104936
• Support remote mode: Support enrich remote mode #104993
• Improve remote enrich: Planning works for remote enrich #105095

RCS 2.0

skip_unavailable

Execution info

Documentation

• Add doc for cross cluster query #105934

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Pinging @elastic/es-ql (Team:QL)

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Pinging @elastic/elasticsearch-esql (:Query Languages/ES|QL)

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Pinging @elastic/es-analytics-geo (Team:Analytics)

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