Add Change type option to work items

What does this MR do and why?

This MR adds ability to change type of project level work items like Objective, Key result, Task and Issues as work items.

The designs are available here. However, the functionality is served as per the comment.

Task	MR link
Add `Change type` to the utility actions menu o... (#474528 - closed)	This MR
Confirmation modal with input required to compl... (#474529 - closed)	This MR
Add validations when a work item is selected fo... (#474530 - closed)	This MR
Add EE and rspecs for change type modal	!175435 (merged)
Add Change type support for work item drawer on... (#501062 - closed)
Add Change type support for work item drawer on... (#501061 - closed)

Limitations:

• If a child item is added/removed in the child item and change type is used, the warning message will not appear upfront without page reload. We need to update the child item cache count in Apollo cache.
• The child items are not handled while changing type. It will be covered as part of #499488
• The parent is not handled while changing type. It will be covered as part of #501424
• Conversion from Issue to Epic is not support. It will be part of #503276
• The option is not available on Epic as it will covered once the backend issue #478486 is cleared.

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

Scenario	Screen recording
With child item
With parent
With non-null fields	Screen Recording 2024-10-28 at 7.45.54 PM.mov
Objective to Key results with no parent or child item	Screen Recording 2024-10-28 at 8.00.10 PM.mov
Key results to Objective with no parent or child item	Screen Recording 2024-10-28 at 8.00.46 PM.mov
Issue to Task with no parent or child item	Screen Recording 2024-10-28 at 8.02.54 PM.mov
Task to Issue with no parent or child item	Screen Recording 2024-10-28 at 8.04.12 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/Objective
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 an option to be converted
7. Check if a warning appears when
   1. there are child items and the Change type button is disabled
   2. there is a parent linked and the Change type button is disabled
   3. there are non-null fields which are not available in the selected work item type
8. Click on Change type button
9. Verify
   1. if the type is changed below the title
   2. if the Close button is showing right text
   3. if the widgets are updated as per the type

Related to #385131 (closed)