Epic Boards - MVC1 bug fixes [RUN AS-IF-FOSS]

What does this MR do?

This includes some small fixes and a refactoring for epic boards.

Requires :epic_boards feature flag.

• Use admin_epic_board_list permission
• Prevent dragging of epic card
• Hide scope in Create board modal
• Hides filter search bar on index page of epic boards

Refactor isEpicBoard state into a getter using issuableType on state, which is a follow up from a previous MR: !55456 (comment 519946336)

Progress of Epic boards feature development

Previous iterations	MR link
Index page	!53100 (merged)
Empty lists	!54169 (merged)
Epics in lists	!54528 (merged)
Multiple epic boards switcher	!54399 (merged)
Create epic board	!54642 (merged)
Display epic reference in card	!55028 (merged)
Add label list	!55011 (merged)
Collapse list and polish	!55456 (merged)

Screenshots (strongly suggested)

No visual changes

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
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  • I have not included a changelog entry because _____.
• Documentation (if required)
• Code review guidelines
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• 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

Related to #323415 (closed)