Disable epic quick actions for new epics

What does this MR do?

Adding/removal of epic links expects that both parent and child epics are created. If parent_epic is applied on a new not-persisted epic, then EpicLink then this epic link is created before target epic is saved which has couple of side-effects:

• CreateService's set_child_epic fails to update the new epic
• no system notes are created
• internal_id for epics is out-of-sync because EpicLink attempts to store new epic (and fails and rolls-back thsi save) -> then internal_id is already set which target epic is saved (as part of regular save operation) but not bumped in DB

Because epic quick actions don't work properly with unpersisted epics, it will be disabled until the code is updated to work properly with new epics.

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

Related to #288811 (closed)