ESQL: define interfaces as contractual extension points

[bpintea]

Description

In order to simplify contributions to the ESQL and limit the surface area (and associated mistakes), we should extract common functionality into dedicated interfaces that consumers can choose to implement. This will allow encapsulating new functionality without the new contributions needing to touch core parts.

The following is a list of (initial) interfaces to implement:

• Post analysis verification (ESQL: Add interfaces to distribute the post-analysis verification #119798)
• Post optimisation verification (ESQL: Rename Validatable iface to PostLogicalOptimizationVerificationAware #119985)
• Query rewriting/translation (ESQL: introduce a pre-mapping logical plan processing step #121260)
• Predicates pushdown to Lucene (ESQL: extend TranslationAware to all pushable expressions #120192)
• License checks (ESQL: Add a LicenseAware interface for licensed Nodes #118931)
• Metrics registration (ESQL: Implement a MetricsAware interface #120527)

[elasticsearchmachine]

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