Status List Server Hardening & Production Readiness

## Overview

This EPIC tracks all work needed to harden the status-list-server for production: ensuring spec compliance with [OAuth Status List draft 21](https://datatracker.ietf.org/doc/draft-ietf-oauth-status-list/), improving infrastructure (CI, Docker, dependencies), enhancing security (auth, key management, caching), increasing flexibility (configurable database, cert provisioning, DNS providers), and improving operability (observability, error handling, API design).

The EPIC also incorporates action items from the architecture review discussion in [#139](https://github.com/adorsys/status-list-server/issues/139), including caching strategy re-evaluation, log collection, least-privilege DB access, and HA considerations.

## References

- Spec: https://datatracker.ietf.org/doc/draft-ietf-oauth-status-list/
- Discussion: https://github.com/adorsys/status-list-server/issues/139