[Feature flag] Enable batch suggestions in MRs

What

Remove the :batch_suggestions 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: @andr3

Expectations

### What are we expecting to happen?

We see the add to batch button on each suggestion. Applying them goes well, individually and in batches.

What might happen if this goes wrong?

Problems when applying batches of suggestions

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 (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