Add OncallRotationUpdate mutation

What does this MR do?

This adds a mutation, OncallRotationUpdate, that allows users to edit their On-Call Rotations. It uses the EditService from !55258 (merged) to do the editing.

Since an edit is similar to a create, this MR also moves a lot of helper methods to be shared between the Create & Update mutations.

Example requests, via http://localhost:3000/-/graphql-explorer:

Request

mutation editRotation($input: OncallRotationUpdateInput!) {
  oncallRotationUpdate(input: $input) {
    oncallRotation {
      id
      name
      startsAt
      length
      lengthUnit
      activePeriod {
       startTime
       endTime
      }
      participants {
        nodes {
          user {
            username
          }
          colorWeight
          colorPalette
        }
      }
    }
    errors
  }
}

Variables

{
  "input": {
    "id": "gid://gitlab/IncidentManagement::OncallRotation/51",
    "name": "test rotation 34",
    "startsAt": {
      "date": "2022-09-19",
      "time": "08:00"
    },
    "rotationLength": {
      "length": 7,
      "unit": "DAYS"
    },
    "participants": []
  }
}

Response

{
  "data": {
    "oncallRotationUpdate": {
      "oncallRotation": {
        "id": "gid://gitlab/IncidentManagement::OncallRotation/51",
        "name": "test rotation 34",
        "startsAt": "2022-09-18T20:00:00Z",
        "length": 7,
        "lengthUnit": "DAYS",
        "activePeriod": {
          "startTime": null,
          "endTime": null
        },
        "participants": {
          "nodes": []
        }
      },
      "errors": []
    }
  }
}

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • I have included a changelog entry.
  • I have not included a changelog entry because _____.
• 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 #262862