feat(tools): Add query_postgres tool for read-only natural language queries to PostgreSQL

[Sagart-cactus]

Description

This PR introduces a new tool, query_postgres, that enables Strands Agents to run read-only SQL queries (SELECT, WITH/CTE) against a PostgreSQL database using natural language.

Key highlights:

• Blocks all write operations (INSERT, UPDATE, DELETE, etc.) for safety
• Uses only environment variables (PGHOST, PGPORT, PGDATABASE, PGUSER, PGPASSWORD) for secure credential management
• Designed for data analytics, dashboards, and business insights use cases
• Includes comprehensive tests covering query validation, environment variable errors, and query execution
• Adds optional dependency psycopg2-binary under [project.optional-dependencies.query_postgres]
• Fully documented with usage examples, environment variable reference, and README integration

Related Issues

Closes #154

Documentation PR

N/A (README updates included in this PR)

Type of Change

• New Tool

Testing

Tool was tested using:

• hatch fmt --linter ✅
• hatch fmt --formatter ✅
• hatch test --all ✅

All tests passed successfully including:

• test_missing_env_vars
• test_disallowed_query
• test_read_only_select (with mocked connection)

Checklist

• I have read the CONTRIBUTING document

• I have added tests that prove my fix is effective or my feature works

• I have updated the documentation accordingly

• I have added an appropriate example to the documentation to outline the feature

• My changes generate no new warnings

• Any dependent changes have been merged and published

• By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[Sagart-cactus]

Not sure why the PR did not assign reviewer for this PR. @zastrowm can you help in reviewing this one too 🙈🙏

[DimitrijeGlibic]

Any updates on this? Do you think it will be merged soon? I’m looking to use it in a project.