Hide default stages and remove custom stages in cycle analytics

What does this MR do?

⚠️ Blocked by !18514 (merged), !18372 (merged) and !18208 (merged)

This MR adds additional functionality to the cycle analytics stage table:

• Hiding default stages (by default 7 stages are created, issue, plan, staging, test, review, production, code)
• Removing custom stages

No changelog added, this will all be released as part of #12196 (closed)

Screenshots

Default Stage	Custom Stage

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

Due to the dependent MRs, the easiest option for testing this locally at the moment is to run !17496 (closed) which includes all the required MRs.

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team