plpgsql function for EXPLAIN of generic plan

Params:

• query (text)
• optionally, format (text -- detault -- or JSON)
• optionally, ideas to verify using hypopg (e.g., index ideas, array of text -- queries)

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Acceptance Criteria

• PL/pgSQL function accepts a query text and returns EXPLAIN output for the generic plan
• Optional format parameter supports text (default) and JSON output
• Optional array of index definitions for HypoPG-based hypothetical index verification
• Function works on PostgreSQL 14+

Definition of Done

• Function is created and tested with various query types
• HypoPG integration tested for index suggestions
• Documentation covers function parameters and usage examples