[ES|QL] High-level AST mutation API

[vadimkibana]

Implement a high-level API for ES|QL AST mutations.

• [x] Ability to add/remove METADATA fields
• [x] Ability to add/remove WHERE commands
• [x] Ability to change LIMIT
• [x] Ability to add/remove SORT command expressions
• [x] Ability to add/remove FROM sources
• [x] Ability to find all STATS new field columns used
• [x] Ability to insert ES|QL params, into places where they are supported.

The API

The API could look something like below.

Manipulate METADATA fields:

// Remove METADATA field
Query.removeFromMetadata('_id');
// Add METADATA field
Query.addFromMetadata('_id');

Remove commands:

Query.removeCommands(node => node.name === 'limit');
// or
Query.removeCommandsByName('limit')

Change LIMIT of the query:

// Change LIMIT to specific value
Query.limit.set(10);
// Remove LIMIT command
Query.limit.remove();

...

[elasticmachine]

Pinging @elastic/kibana-esql (Team:ESQL)