[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?
<!-- Which dashboards from https://dashboards.gitlab.net are most relevant? -->
## 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
- [x] 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](https://docs.gitlab.com/ee/development/feature_flags/controls.html#cleaning-up) by running chatops command in `#production` channel
issue