Make Puma enabled by default for everyone

We continue battle testing Puma and figuring out the best defaults that is reflect in number of issues and epics:

• enable of Puma on dev.gitlab.org: gitlab-com/gl-infra&82 (closed),
• enable of Puma on gitlab.com: gitlab-com/gl-infra&78 (closed)

This issue is to track the effort to make Puma on by default for everyone.

• Ensure that this runs on gitlab.com for at least one full release,
• Allow to update db_pool: omnibus-gitlab#4631 (closed)
• Update and close benchmarks: https://gitlab.com/gitlab-org/gitlab-ce/issues/62878, https://gitlab.com/gitlab-org/gitlab-ce/issues/62876
• Handle zero-downtime deployments with Puma: omnibus-gitlab#4739 (closed)
• Chronic Duration is not thread-safe: https://gitlab.com/gitlab-org/gitlab-ce/issues/66637
• Enable Puma fleet-wide on GitLab.com: gitlab-com/gl-infra/production#1684 (closed)
• Improve Puma request handling in multi-threaded mode: #36858 (closed)
• Improve graceful restart handling in Omnibus: omnibus-gitlab#4756 (closed)
• Do full restart of Puma during deployment: omnibus-gitlab#4928 (closed)
• Add optional Puma support to GitLab Chart: gitlab-org/charts/gitlab#1313 (closed)
• Upstream Puma multi-threading patches: #196002 (closed)
• Update relevant documentation: https://gitlab.com/gitlab-org/gitlab-ce/issues/66947
• Update Omnibus defaults: omnibus-gitlab#3896 (closed)
• Disable Rugged in Puma: #35371 (closed)
• Update HA documentation: omnibus-gitlab#5091 (closed)
• Ensure that Puma is on by default (Omnibus change): omnibus-gitlab#4698 (closed)
• Ensure that Puma is on by default (GitLab Chart change): gitlab-org/charts/gitlab#1908 (closed)

All issues with Multithreaded App Server: https://gitlab.com/groups/gitlab-org/-/issues?scope=all&utf8=%E2%9C%93&state=opened&label_name[]=Multithreaded%20App%20Server