added metadata section to platforms and platform groups config

[wxtim]

These changes close #4528

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).
• Applied any dependency changes to both setup.cfg and conda-environment.yml.
• Does not need tests (Config change).
• Appropriate change log entry included.
• No documentation update required, yet. See cylc config --list-platforms #4557

[hjoliver]

Looks good. Just wondering about a few things though:

• worth putting the common descriptive text in a string constant?
• would a short-cut option would be useful (e.g. --describe-platforms) that just prints platform names and metadata?
• there's no internal use for this, so I wonder if a single meta (or description?) item would suffice, rather than a section for multiple arbitrary items? (I suppose it's possible that individual items that can be extracted separately could be useful at a site ... e.g. cost per cpu hour or something?).

[wxtim]

* worth putting the common descriptive text in a string constant?

Yes

* would a short-cut option would be useful (e.g. `--describe-platforms`) that just prints platform names and metadata?

I think so; see #4557 - I'm think that I'm going to take your comment as a yes to the question in that ticket.

* there's no internal use for this, so I wonder if a single `meta` (or `description`?) item would suffice, rather than a section for multiple arbitrary items?  (I suppose it's possible that individual items that can be extracted separately could be useful at a site ... e.g. `cost per cpu hour` or something?).

It would, but I think it's reasonable to leave it open ended - examples might include

[meta]
description = """
Our Cluster.
"""
url=http://somedocs.internalwebsite.com
max-memory-request=200G
max-cpu-request=12

Though to be honest, I'm not completely convinced that this is required.

[wxtim]

@hjoliver : I think I've now

• added the description field.
• justified my decision to leave other fields open ended[1].
• Created a new ticket to discuss the platform listing.

[1] Just because Cylc has no internal use for formally defined fields doesn't mean that someone else can't use them. For example, my personal workflows repo has a script which GH actions uses to extract metadata and dump it in the repo README.md. I could put the formal fields I want into a single description box and parse them in the same way, but it seems nicer to have them as metadata in the config.

[hjoliver]

added the description field.

I think you might have misinterpreted my comment on this, which was:

worth putting the common descriptive text in a string constant?

I meant, this descriptive text is identical for platform and group:

                Allows writers of platform configurations to add information
                about platform usage. There are no-preset items because
                Cylc does not use any platform metadata internally.

                Users can then see information about defined platforms using::

                   cylc config -i [platforms]

                .. seealso::
                   :ref:`AdminGuide.PlatformConfigs`

... so, it should really be stored in a string constant to avoid the duplication.

Also, There are no-preset items is now not true since you've added a preset description item (which I don't think we need, if going with the arbitrary metadata solution).

[wxtim]

@hjoliver - completely got the wrong end of the stick here - have pushed another commit which hopefully hits nearer the mark.

[hjoliver]

That's got it, thanks @wxtim