[Feature flag] Enable flag for the Configurable defaults for "Squash commits" option feature

What

Remove the :squash_options feature flag ...

Owners

• Team: Create: Source Code
• Most appropriate slack channel to reach out to: #g_create_source-code
• Best individual to reach out to: @sming-gitlab

More info

• Feature issue #17613 (closed)
• Docs https://docs.gitlab.com/ee/user/project/merge_requests/squash_and_merge.html#squash-commits-options

Expectations

What are we expecting to happen?

Showing an option to set the default behaviour for the the squash commits feature

What might happen if this goes wrong?

Something in the squashing not working as expected.

What can we monitor to detect problems with this?

Reports of issues related with squash

https://gitlab.com/gitlab-org/gitlab/-/issues?scope=all&utf8=%E2%9C%93&state=opened&search=squash

Beta groups/projects

If applicable, any groups/projects that are happy to have this feature turned on early. Some organizations may wish to test big changes they are interested in with a small subset of users ahead of time for example.

• (personal projects where engineers have ownership to change the settings)
• ...

Roll Out Steps

• Enable on staging
• Test on staging
• Ensure that documentation has been updated
• Enable on GitLab.com for individual groups/projects listed above and verify behaviour
• Coordinate a time to enable the flag with #production and #g_delivery on slack.
• Announce on the issue an estimated time this will be enabled on GitLab.com
• Enable on GitLab.com by running chatops command in #production
• Cross post chatops slack command to #support_gitlab-com (more guidance when this is necessary in the dev docs) and in your team channel
• Announce on the issue that the flag has been enabled
• Remove feature flag and add changelog entry
• After the flag removal is deployed, clean up the feature flag by running chatops command in #production channel