Draft: Experiment: Support requirement IIDs starting with REQ-

What does this MR do?

This MR allows requirement IIDs to change format from ^\d+$ (e.g. 7) to ^REQ-\d+$ (e.g. REQ-7). Either can be used for input, but output will only return ^REQ-\d+$.

Sample queries

Find one requirement

query {
  project(fullPath: "group/project_path") {
    requirements(iid: "REQ-7") {
      nodes {
        iid
        title
      }
    }
  }
}

This also works:

query {
  project(fullPath: "group/project_path") {
    requirements(iid: "7") {
      nodes {
        iid
        title
      }
    }
  }
}

Both result in:

{
  "data": {
    "project": {
      "requirements": {
        "nodes": [
          {
            "iid": "REQ-7",
            "title": "seventh requirement"
          }
        ]
      }
    }
  }
}

Find multiple requirements

query {
  project(fullPath: "group/project_path") {
    requirements(iids: ["REQ-7", "REQ-1", "REQ-2"]) {
      nodes {
        iid
        title
      }
    }
  }
}

Either format will work:

query {
  project(fullPath: "group/project_path") {
    requirements(iids: ["REQ-7", 1, "2"]) {
      nodes {
        iid
        title
      }
    }
  }
}

Will result in:

{
  "data": {
    "project": {
      "requirements": {
        "nodes": [
          {
            "iid": "REQ-7",
            "title": "seventh requirement"
          },
          {
            "iid": "REQ-1",
            "title": "first requirement"
          },
          {
            "iid": "REQ-2",
            "title": "second requirement"
          }
        ]
      }
    }
  }
}

Update query

This is valid:

mutation { updateRequirement
  (input: 
    { projectPath: "group/project_path", 
      title: "updated requirement using iid", 
      iid: "REQ-7"}) {
    requirement {
      iid
      title
	  }
    errors
  }
}

This is equivalent:

mutation { updateRequirement
  (input: 
    { projectPath: "group/project_path", 
      title: "updated requirement using iid", 
      iid: "7"}) {
    requirement {
      iid
      title
	  }
    errors
  }
}

Both result in:

{
  "data": {
    "updateRequirement": {
      "requirement": {
        "iid": "REQ-7",
        "title": "updated requirement using iid"
      },
      "errors": []
    }
  }
}

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

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• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
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Security

Does this MR contain changes to processing or storing of credentials or tokens, authorization and authentication methods or other items described in the security review guidelines? If not, then delete this Security section.

• 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 #323779 (closed)