schema: separate task and job mutations

[oliver-sanders]

Separate task and job mutations in the schema.

• This means you can now selectively kill/poll specific jobs by explicitly providing the submit number.
• However, for regular use there is no interface change.
• This allows the UI to perform mutations on jobs (e.g. right click on running job icon, select kill) (see mutations in the tree view cylc-ui#504).

At present there isn't much value to being able to specify a particular job submit number since it would be considered an error for two jobs to run at the same time.

Here's an example specifying the job submit num on the CLI:

$ # cylc kill <flow> '<namespace>.<point>#<job>'
$ cylc kill abc 'foo.1#1'

And here via GraphQL:

mutation () {
    kill ("abc", "foo.1#1") {
        result
    }
}

Obviously # isn't ideal for use on the CLI, we could consider something else, see also #3592.

Requirements check-list

• I have read CONTRIBUTING.md and added my name as a Code Contributor.
• Contains logically grouped changes (else tidy your branch by rebase).
• Does not contain off-topic changes (use other PRs for other changes).

• Appropriate tests are included (unit and/or functional).
• Already covered by existing tests.
• Does not need tests (why?).

• Appropriate change log entry included.
• No change log entry required (why? e.g. invisible to users).

• (master branch) I have opened a documentation PR at cylc/cylc-doc/pull/XXXX.
• (7.8.x branch) I have updated the documentation in this PR branch.
• No documentation update required.

• Created an issue at cylc-flow conda-forge repository with version changes (if you changed dependencies in setup.py, see recipe/meta.yaml).
• No dependency changes.

[oliver-sanders]

This input type enables us to tell that this mutation works on jobs by flicking through the results of an introspection query.

[oliver-sanders]

This replaces TaskPool._parse_task_item.

[oliver-sanders]

Closing this now, will bring back in a new form with the universal identifier.