Stablize register spec

What does this MR do?

Stablizes register spec by:

1. Retrying the complete signup process (current retry mechanism was broken because if signup was expected to fail but succeeded, the retry would assume that we are on the register page and try to fill in the fields)
2. Retry enable_require_admin_approval_after_user_signup_via_ui
3. Give more time for require_admin_approval_after_user_signup to kick in.

Closes #294188 (closed)

Conformity

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

Availability and Testing

• [-] Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

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