Refactor client/server & GraphQL workflow mutations

[MetRonnie]

These changes partially address https://github.com/cylc/cylc-uiserver/issues/271

Sibling: https://github.com/cylc/cylc-uiserver/pull/290

• Refactored the message format sent from server to client. Instead of just the raw result of the GraphQL mutation (or whatever request was sent[^1]), the server now responds with a tuple of (content, error, user)
  • This allows errors to be returned over the ZMQ socket without mixing/confusing with the data content
  • user is included like this instead of adding it to the GraphQL {data: ..., errors: ...} response (the spec does not permit adding extra keys)
  • A NamedTuple called ResponseTuple is used instead of a regular tuple for better clarity and type safety
• RefactoredGraphQL workflow mutation output type. Instead of the sometimes-inconsistent GenericResponse output which could be any object in practice, the output is now a graphene.List of GenericReponses, and GenericResponse has 3 fields: workflowId = graphene.String(), success = graphene.Boolean() and message = graphene.String()
  • This pins down what the expected response should be, which should avoid traceback issues like https://github.com/cylc/cylc-uiserver/issues/271
  • In practice this looks like:

    mutation {
      hold (
        workflows: ["temp4"]
        tasks: ["foo.2"]
      ) {
        results {
          workflowId
          success
          message
        }
      }
    }
    

    {
      "data": {
        "hold": {
          "results": [
            {
              "workflowId": "rdutta|temp4",
              "success": true,
              "message": "Command queued"
            }
          ]
        }
      }
    }
    

[^1]: The exception to this is that Protobuf results are sent back as-is in bytes format instead of the tuple, because bytes is not JSON-serializable

Requirements check-list

• [x] I have read CONTRIBUTING.md and added my name as a Code Contributor.
• [ ] Contains logically grouped changes (else tidy your branch by rebase).
• [x] Does not contain off-topic changes (use other PRs for other changes).
• [x] Applied any dependency changes to both setup.py and conda-environment.yml.
• [ ] Appropriate tests are included (unit and/or functional).
• [ ] Appropriate change log entry included.
• [ ] (master branch) I have opened a documentation PR at cylc/cylc-doc/pull/XXXX.

[MetRonnie]

So looks good.. Few minor comments below..

The main issue I'm having (when trying to run this and the UIS sibling), is getting it working

Sorry, should have mentioned: It's not working from the UI yet as some changes need to be made there. But it's working in GraphiQL.

[MetRonnie]

Not going to be finished by Christmas so bumping to 8.0rc2