feat: add Docker-based PostgreSQL setup as an alternative to manual installation

[olcortesb]

What

Add Docker-based PostgreSQL setup as an alternative to manual installation.
Includes docker-compose.yml and documentation in docs/local-postgres-setup.md.

Why

Simplifies local development setup — one command to get PostgreSQL running
instead of manual RPM installation and initdb configuration.

Testing done

• docker compose up -d starts PostgreSQL
• ./target/release/extenddb init --pg-user postgres --pg-pass extenddb-local-dev succeeds
• ./target/release/extenddb serve starts and curl -sk https://127.0.0.1:8000/health returns healthy
• AWS CLI operations work against the running instance
• docker compose down

python3 docs/build-docs.py

Done: 18 HTML, 18 PDF built, 0 skipped/failed.
Output: /home/ackstorm/workspace/extenddb/docs/rendered/
~/workspace/extenddb (main *)$ 

Checklist

• I have read CONTRIBUTING.md
• All tests pass (cargo test --workspace)
• Code is formatted (cargo fmt --check)
• Clippy is clean (cargo clippy -- -W clippy::pedantic)
• [ N/A ] I have added or updated tests for new functionality
• [ N/A ] I have updated documentation if behavior changed
• [ N/A ] Breaking changes are noted below (if any)

By submitting this pull request, I confirm that my contribution is made under
the terms of the Apache License 2.0 and I agree to the Developer Certificate of
Origin (DCO). See CONTRIBUTING.md for details.

[LeeroyHannigan]

Thanks for the contribution @olcortesb! The docker-compose approach is clean and well-documented, we appreciate the thoroughness of the testing you did.

We're currently evaluating the best path for local development setup (Docker, native, or a combination), so we're going to keep this PR open while we finalize that direction. We don't want you to feel like this is being ignored, it's genuinely useful work and may well land as-is or with minor adjustments once we settle on the approach.

We'll update this PR once we have a decision. Thanks for your patience! 🙏

[olcortesb]

Thanks for the contribution @olcortesb! The docker-compose approach is clean and well-documented, we appreciate the thoroughness of the testing you did.

We're currently evaluating the best path for local development setup (Docker, native, or a combination), so we're going to keep this PR open while we finalize that direction. We don't want you to feel like this is being ignored, it's genuinely useful work and may well land as-is or with minor adjustments once we settle on the approach.

We'll update this PR once we have a decision. Thanks for your patience! 🙏

Hi @LeeroyHannigan , thanks for your comment! Don't worry—please let me know if I can help by updating this or creating a new pull request.