Create an issue board via GraphQL mutation

What does this MR do?

It adds a GraphQL mutation that adds support for creating an issue board.

Multiple issue boards for groups are supported only for at least premium license.

Examples

Request

mutation {
  createBoard(input: {projectPath: "flightjs/flight", name: "test board"}) {
    board {
      id
      name
    }
    errors
  }
}

Response

{
  "data": {
    "createBoard": {
      "board": {
        "id": "gid://gitlab/Board/4",
        "name": "test board"
      },
      "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.

Issue: #233433 (closed)