scripts: add Jenkins unit test analysis tool

scripts: add Jenkins unit test analysis tool

Add analyze_unittest_jenkins.py to aggregate and analyze unit test
results across multiple Ceph PRs by mining Jenkins CI build logs.

The script fetches recent open PRs from GitHub, extracts Jenkins build
URLs from PR checks, downloads console logs in parallel, and parses
CTest output to generate comprehensive failure reports.

This enables data-driven decisions about test infrastructure
improvements and helps identify systemic issues in the test suite.

Fixes: https://tracker.ceph.com/issues/76513
Assisted-by: IBM Bob (Claude 3.7 Sonnet)
Signed-off-by: Steven Zuraski <steven.zuraski@ibm.com>