Update approvers dropdown to use new endpoint

Issue: #28902 (closed)

What does this MR do?

This MR doesn't change any of the existing UI/UX. The only thing done here is updating it to use the new /projects/:id/groups (BE MR: !53642 (merged))

new-api-endpoint

So now, it will just return the groups that the project belongs to.

(For more info on how the logic in determining the groups, you can see a detailed break down here > #28902 (comment 502684120))

Testing Case

In order to see the groups, we need to create a group and then a project.

1. Create a new group
2. Create a project belonging to that group

• The group that this project belongs to will appear:

☝ This project belongs to a group named Public Project Group

• If a project doesn't belong to a group, no groups will appear:

☝ This project does not belong to a group, it belongs to the user Administrator

• If a group has been selected, it will not reappear in the dropdown (similar to the current/previous behaviour):

skip_groups

Screenshots (strongly suggested)

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

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