Log feature flag deletions in feature-flag-log project

Preamble

In !88 (merged) we've added the ability to log feature flag changes as issues in https://gitlab.com/gitlab-com/gl-infra/feature-flag-log/-/issues?scope=all&utf8=%E2%9C%93&state=closed project 👍

Problem

However, we don't log any feature flag deletions. This could be useful because deleting an disabled/enabled feature flag is also an implicit value change and should be logged.

Solution

Log a feature flag deletion so they show up in https://gitlab.com/gitlab-com/gl-infra/feature-flag-log/-/issues?scope=all&utf8=%E2%9C%93&state=closed.

Example

Feature flag incident_sla_dev has been changed a few times and recently deleted via Slack:

No record of this deletion is found in the feature-flag-log project.