Cleanup: Reduce feature flag process documentation
https://docs.gitlab.com/ee/development/feature_flags/process.html#feature-flags-in-gitlab-development is quite confusing:
- It never mentions enabling the flag in production globally.
- It doesn't mention the roll out issue template (https://gitlab.com/gitlab-org/gitlab/-/blob/master/.gitlab/issue_templates/Feature%20Flag%20Roll%20Out.md).
It does link to https://docs.gitlab.com/ee/development/feature_flags/development.html, which suggests the roll out template.
I think we should reduce this documentation, or even remove it entirely. Currently it's out of sync with the rest of the docs and the issue template, and it's hard for people to know what the right approach is. Ideally we would have a single source of truth and just link to that.
Edited by Kamil Trzciński (Back 2025-01-01)