ci: enable dd merge queue (#10895)

This PR will enable the Datadog merge queue in this repo. See details in
the Devflow docs
[here](https://datadoghq.atlassian.net/wiki/spaces/DEVX/pages/3121612126/MergeQueue#Configuration-Specification).

## 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
- [ ] 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)

repository.datadog.yml

@@ -1,4 +1,9 @@
 ---
 schema-version: v1
 kind: mergequeue
-enable: false
+enable: true
+workflow_type: noqueue # TODO: change to speculative once stable
+merge_method: squash
+gitlab_check_enable: true
+gitlab_jobs_retry_enable: true
+gitlab_fail_fast: true