Process: Enable merge queue to speed up integration

[dmihalcik-virtru]

Problem: We currently require up-to-date checks and all-green CI tests, which means that CI has to run between any updates and before clicking merge.

BUT: We currently manage our GitHub projects with terraform, and the provider does not support merge queues.

integrations/terraform-provider-github#1481

Mitigations:

1. Speed up integration tests
2. Reduce number of tests that run to only match changed files (e.g. don't run full CI on readme changes)
3. Enable the 'auto-merge' option

[pflynn-virtru]

A merge queue helps increase velocity by automating pull request merges into a busy

branch and ensuring the branch is never broken by incompatible changes.

The merge queue provides the same benefits as the Require branches to be up to date before merging branch protection, but does not require a pull request author to update their pull request branch and wait for status checks to finish before trying to merge.

Using a merge queue is particularly useful on branches that have a relatively high number of pull requests merging each day from many different users.

Definitely needed in this repo.

[strantalis]

@dmihalcik-virtru @pflynn-virtru I can go ahead and enable this on main. Do we need to update our workflows for this to work?

https://docs.github.com/en/repositories/configuring-branches-and-merges-in-your-repository/configuring-pull-request-merges/managing-a-merge-queue#triggering-merge-group-checks-with-github-actions