[Feature flag] Enable flag to disable alternate refs in fetches

What

Enable the gitaly_fetch_internal_no_alternate_refs feature flag, which causes us to ignore alternate refs on fetches. This should speed up internal fetches.

Owners

• Team: Gitaly
• Most appropriate slack channel to reach out to: #g_create_gitaly
• Best individual to reach out to: pks-t

Expectations

What release does this feature occur in first?

%14.2

What are we expecting to happen?

All internal fetches should be sped up.

What might happen if this goes wrong?

Internal fetches start to fail.

What can we monitor to detect problems with this?

Observe feature status for the following RPCs:

• ResolveConflicts
• UserCommitFiles
• UserRevert
• FetchInternalRemote
• FetchSourceBranch

Roll Out Steps

• Read the documentation of feature flags
• Add featureflagstaging to this issue (howto)
• Is the required code deployed? (howto)
• Do we need to create a change management issue? (howto)
• Enable on staging (howto)
• Test on staging (howto)
• Verify the feature flag was used by checking Prometheus metric gitaly_feature_flag_checks_total
• Announce on this issue an estimated time this will be enabled on GitLab.com
• Add featureflagproduction to this issue
• Enable on GitLab.com by running chatops command in #production (howto)
• Cross post chatops slack command to #support_gitlab-com and in your team channel
• Verify the feature flag is being used by checking Prometheus metric gitaly_feature_flag_checks_total
• Announce on the issue that the flag has been enabled
• Did you set the feature to both 100% and true (howto)
• Submit a MR to have the feature OnByDefault: true and add changelog entry (howto)
• Have that MR merged
• Possibly wait for at least one deployment cycle (howto)
• Submit an MR to remove the pre-feature code from the codebase and add changelog entry (howto)
• Have that MR merged
• Remove the feature flag via chatops (howto)
• Close this issue