feat (ai-optimizer) : Implement PostgreSQL EXPLAIN plan collection pipeline

[sarthaksarthak9]

Description

This PR introduces the initial implementation of the EXPLAIN plan collection pipeline for the AI-assisted PostgreSQL query optimization framework.

The collector identifies slow query candidates from pg_stat_statements, captures execution plans using EXPLAIN (ANALYZE, BUFFERS, FORMAT JSON), and persists the collected plans and metadata in the ai_optimizer schema for downstream analysis and recommendation generation.

To minimize impact on production workloads, the collector is designed to operate against a PostgreSQL read replica and supports configurable execution thresholds and collection intervals.

Collection workflow

• Retrieves candidate queries from pg_stat_statements
• Filters candidates using configurable thresholds
• Executes EXPLAIN (ANALYZE, BUFFERS, FORMAT JSON)
• Captures execution plans and collection metadata
• Records collection errors for troubleshooting

Notes

• Recommendation generation, validation workflows, and API integration will be implemented in subsequent phases.
• Runtime verification of the management command was not possible in the current environment because the required Django dependencies are unavailable.