docs: add pre-release performance gate runbook to release doc (#14188)

Adding the runbook documentation for our pre-release performance gating
to the release documentation.

## Checklist
- [x] PR author has checked that all the criteria below are met
- The PR description includes an overview of the change
- The PR description articulates the motivation for the change
- The change includes tests OR the PR description describes a testing
strategy
- The PR description notes risks associated with the change, if any
- Newly-added code is easy to change
- The change follows the [library release note
guidelines](https://ddtrace.readthedocs.io/en/stable/releasenotes.html)
- The change includes or references documentation updates if necessary
- Backport labels are set (if
[applicable](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting))

## Reviewer Checklist
- [x] Reviewer has checked that all the criteria below are met 
- Title is accurate
- All changes are related to the pull request's stated goal
- Avoids breaking
[API](https://ddtrace.readthedocs.io/en/stable/versioning.html#interfaces)
changes
- Testing strategy adequately addresses listed risks
- Newly-added code is easy to change
- Release note makes sense to a user of the library
- If necessary, author has acknowledged and discussed the performance
implications of this PR as reported in the benchmarks PR comment
- Backport labels are set in a manner that is consistent with the
[release branch maintenance
policy](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting)

Author: erikayasuda

docs/contributing-release.rst

@@ -16,6 +16,35 @@ Prerequisites
 
 2. Ensure the CI is green on the branch on which the release will be based.
 
+3. Ensure there are no SLO breaches on the release branch (``main`` for new major/minor, ``major.minor`` branch for patch releases). See section below for details.
+
+Pre-Release Performance Gates
+-----------------------------
+
+This repository is using pre-release performance quality gates.
+
+On ``main`` or the ``major.minor`` release branch, verify that the latest CI pipeline passed the ``check-slo-breaches`` job.
+If any SLO is breached, the release pipeline on GitLab will be blocked.
+See our thresholds file(s) at `bp-runner.macrobenchmarks.fail-on-breach.yml <https://github.com/DataDog/dd-trace-py/blob/3cf3342a005c1ef9e345d2a82a631bc827c8617a/.gitlab/benchmarks/bp-runner.macrobenchmarks.fail-on-breach.yml>`_ and `bp-runner.microbenchmarks.fail-on-breach.yml <https://github.com/DataDog/dd-trace-py/blob/3cf3342a005c1ef9e345d2a82a631bc827c8617a/.gitlab/benchmarks/bp-runner.microbenchmarks.fail-on-breach.yml>`_.
+
+There are a few ways to resolve this and unblock the release.
+
+**Prerequisite**
+
+Find the change(s) that contributed the most to performance regression.
+You can check from the `Benchmarking Platform - Benchmarks tab <https://benchmarking.us1.prod.dog/benchmarks?projectId=3&ciJobDateStart=1753290587498&ciJobDateEnd=1753895387498&gitBranch=main>`_ and filter by project and branch to see these commits.
+Notify the authors in `#apm-python-release <https://dd.enterprise.slack.com/archives/C04MK6NNDG9>`_ to see if there are any easy fixes (less than a day of work) that can be pushed to the release branch.
+
+1. **Merge a fix to resolve the performance regression.**
+   This should be considered first, and owned by the author(s) for the change(s) that introduced significant performance regression(s).
+2. **Revert the change(s) that contributed the most to performance regression.**
+   This should be considered if the regression is not acceptable, but the fix will take longer than a day to merge to the release branch.
+3. **Bump the SLO(s) to accommodate for the regressions.**
+   This should only be considered if the regressions are reasonable for the change(s) introduced (ex - new feature with expected overhead, crash fixes, major security issues, etc.).
+   When updating the SLO thresholds, authors must add a comment to their PR justifying the trade offs.
+   See `Performance quality gates - User Guide <https://datadoghq.atlassian.net/wiki/spaces/APMINT/pages/5158175217/Performance+quality+gates+-+User+Guide>`_ for more details.
+
+
 Instructions
 ------------