Enable :cd_skipped_deployment_status by default

What does this MR do?

After a successful rollout on GitLab.com via #283884 (closed), this feature flag should be enabled by default.

Given it will be enabled by default, this MR also adds the new status to the deployments API documentation, which was identified as missing in !46614 (merged).

The feature flag should be removed after one release cycle if no incidents or complaints are received by self-hosted customers.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content