feat(stovepipe): add request log table

[mnoah1]

Summary

Intent:

• Persist immutable request states and explanatory lifecycle occurrences in the internal Stovepipe request log.
• Keep storage terminology and metadata handling aligned with SubmitQueue while supporting the public history API from feat(stovepipe): add request history protobuf contract #638.

Changes:

• Add an append-only MySQL request_log table with stable occurrence identity.
• Keep core lifecycle values in columns and store occurrence-specific context in a non-null JSON metadata column.
• Remove dedicated superseding-request, build-ID, and fact-degree columns.
• Index records for bounded, complete per-request reads.
• Include request-log data in integration database cleanup.

Test Plan

• Loaded all Stovepipe schemas into an isolated MySQL 8 database.
• Inserted representative request-log records and exercised chronological retrieval.
• ./tool/bazel test //stovepipe/extension/storage/mysql/...
• make lint check-tidy check-gazelle

Revert Plan

Revert this PR and remove the unused table before deploying code that writes request-log records.

Jira Issues

None.