GraphQL mutation for moving epics between lists

What does this MR do?

There are 2 main parts of this MR:

• the preparation part extracts code that can be used also for epics from Boards::Issues::MoveService to a separate class and reuses it for Boards::Epics::MoveService. It also removes rubocop offenses.
• the user-faacing part adds a new mutation that adds support for moving an epic between lists on a board

GraphQL request

mutation {
  epicMoveList(input: {boardId: "gid://gitlab/Boards::EpicBoard/1", epicId: "gid://gitlab/Epic/22", fromListId: "gid://gitlab/Boards::EpicList/1", toListId: "gid://gitlab/Boards::EpicList/3"}) {
    errors
  }
}

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.

Related to #233440 (closed)