[Feature flag] Remove feature flag for "Create issue" from alert detail page

What

Remove the :alert_management_create_alert_issue feature flag so that the feature is generally available.

See #217746 (closed)

Owners

• Team: Montor:Health
• Most appropriate slack channel to reach out to: #g_monitor_health
• Best individual to reach out to: @ck3g

Expectations

What are we expecting to happen?

It shows Create button/View issue on the Alerts details page.

What might happen if this goes wrong?

Users cannot create an issue after clicking this button.

What can we monitor to detect problems with this?

We can dig through Kibana logs.

Beta groups/projects

We did not consider enabling this feature per project from the start.

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