Create epic board lists

What does this MR do?

Allows creation of epic board lists in GraphQL API (plus adds create service). Because most/all of logic is shared with issue board lists, it moves existing issue board lists creation logic into a shared parent class which is then reused by issue/epic board lists.

Sample mutation (from staging):

mutation {
  epicBoardListCreate(input: { boardId: "gid://gitlab/Boards::EpicBoard/1", labelId: "gid://gitlab/GroupLabel/2183694"}) {
    errors
    list {
      id
      label {
        id
      }
    }
  }
}

Related to #230985 (closed)

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