Release `require_email_verification`
## Why are we doing this work?
The `require_email_verification` feature flag is currently enabled across all environments.
This feature was first released in [2022](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/86352).
As part of the next steps, the following actions are required:
1. Documentation Update: The relevant documentation must be updated to reflect the current state of the feature.
2. Functional Tests:
- We may need a mechanism to disable the feature flag in existing functional tests.
- Alternatively, we may need to modify the functional tests to ensure they continue to pass in a deterministic manner, accounting for the feature's presence or absence.
3. Feature Flag Removal: To complete the feature's release, we will remove the feature flag and deploy the code that was previously gated by it.
| chatops | dev | staging | staging-ref | production |
| ------- | --- | ------- | ----------- | ---------- |
| `/chatops run feature get require_email_verification --dev --staging --staging-ref --production` | does not exist | does not exist | enabled | enabled |

## Relevant links
* [Chatops](https://gitlab.slack.com/archives/C101F3796/p1739297968454069)
* [Definition](https://gitlab.com/gitlab-org/gitlab/-/blob/ad897fcad1d910c2e257ea2faf96e9541db16002/config/feature_flags/development/require_email_verification.yml)
* [Rollout Issue](https://gitlab.com/gitlab-org/gitlab/-/issues/364835)
* [Feature issue](https://gitlab.com/gitlab-org/modelops/anti-abuse/pipeline-validation-service/-/issues/100/)
* [Introduced By](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/86352)
## Implementation plan
* [ ] Update the documentation
* [ ] Complete the steps in the rollout issue
* [ ] Enable the feature flag in the dev environment
* [ ] Enable the feature flag in the staging-ref environment
* [ ] Delete the feature flag YAML definition and release the code gated by this flag.
## Verification steps
* [ ] The QA tests for the govern stage should continue to pass
* [ ] The YAML definition for the feature flag is deleted from the codebase.
* [ ] The feature works as expected. (TODO:: Determine what the expected behaviour is)
issue