Support Promote Issue to Epic within Change type modal

What does this MR do and why?

This Merge Request implements the ability to "promote" a Work Item Issue to an Epic, including the necessary namespace change to move the issue to the parent group.

To address this, a "promote" action is introduced to convert an issue into an epic while changing its location to the parent group.

⚠️ Note: This is a temporary change till we figure out BE: Add change type support for work item epics (#478486). This functionality is behind work_items_beta and has some limitations

1. The Epic option is visible to all the users similar to other options. Due to that, the option is available, but the API will throw an error on submitting the form. This will change after !177416 (merged) is merged. It will be available to
   1. issues where epic feature is available on group level
   2. user can create epic
2. There are no permissions check for the Change type action on the frontend. It will be covered by the issue #512390 (closed).

References

Please include cross links to any resources that are relevant to this MR. This will give reviewers and future readers helpful context to give an efficient review of the changes introduced.

• This issue #503276 (closed)
• Main issue #385131 (closed)
• The MR thread !166879 (comment 2199754119)

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

Screen Recording 2025-01-09 at 3.55.24 PM.mov

How to set up and validate locally

Prerequisites:

1. Enable the OKRs feature as mentioned in the OKRs docs (e.g. ::Feature.enabled?(:okrs_mvc, Project.find(<PROJECT_ID>)) and the namespace must have Ultimate plan).
2. Enable FF work_items_beta

Steps to verify:

1. Login with any user
2. Go to Project > Issues
3. Open or create an Issue
4. In the kebab menu on top-right, find the Change type action
5. Click on the Change type action to open a modal with related options
6. Select Epic (Promote to group)
7. Click on Change type button
8. Verify if an Epic is created and redirected to it and the original issue is closed

Related to #503276 (closed)