[Feature flag] Enable Sourcegraph

What

First, let's enable the :sourcegraph feature flag. After confirming the stability of the feature, then let's remove the flag for general availability...

Owners

• Team: Create, Editor
• Most appropriate slack channel to reach out to: #s_create
• Best individual to reach out to: @pslaughter (or @andr3 if OOO)

Expectations

What are we expecting to happen?

• This should reveal the admin settings Integrations > Sourcegraph. We will manage setting this up in an infra issue.

What might happen if this goes wrong?

It's possible (but tested for and unlikely) that we start making requests to sourcegraph.com on user accounts that have not opted in to the feature.

What can we monitor to detect problems with this?

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.

• gitlab-org/gitlab project

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 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