doc: document the releng-audit workflow and update release examples

doc: document the releng-audit workflow and update release examples

Updates SubmittingPatches-backports.rst and development-workflow.rst to
capture the new automated backport auditing system.

Changes include:
- Documenting the CI checks for commit parity, conflict simulation, and
  Redmine linkage.
- Explaining how PR authors can trigger a retest (`/audit retest`) and
  how leads can bypass the audit (`/audit override`).
- Replacing outdated `master` branch references with `main`.
- Updating the release cycle timeline to reflect current releases
  (Quincy, Reef, Squid, Tentacle).
- Removing obsolete instructions for manual PR labeling.

Signed-off-by: Patrick Donnelly <pdonnell@ibm.com>