release: v0.28.0 and configurable tokenization batch limit

[allisson]

This commit prepares the v0.28.0 release and adds a configurable limit for batch tokenization operations.

• Update version to v0.28.0 and update CHANGELOG.md with release notes.
• Add TOKENIZATION_BATCH_LIMIT configuration (default: 100).
• Enforce batch limit in TokenizationHandler for tokenize/detokenize.
• Update docs/openapi.yaml with v0.28.0 changes and new parameters.
• Archive related conductor tracks (batch_limit_config and release_v0.28.0).

V0.28.0 Key Changes:

• Batch tokenization limit configuration.
• Individual transit/tokenization key retrieval APIs.
• Atomic batch tokenize/detokenize endpoints.
• Audit log filtering by client_id.
• Configurable Metrics Server timeouts and DB connection settings.
• Client secret rotation with token revocation.
• Strict capability validation and key deletion by name.
• Rate limiter resource leak fix.