Add the option to provide a groupname and only see its' members in occ group:list

[Keeper-of-the-Keys]

Summary

As the title states this adds an optional groupname argument to occ group:list so you can see the members of just that group.

Now you can do occ group:list groupname

If the change is welcome I can work on the further needed steps to get it in.

TODO

1. Fail/return error if group doesn't exist
2. Only print the members and not the groupname

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
  - [ ] Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[Keeper-of-the-Keys]

@joshtrichards Hey thanks for tagging/milestoning!

Is there anything I can do to help move things along?

[github-actions]

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[welcome]

Thanks for your first pull request and welcome to the community! Feel free to keep them coming! If you are looking for issues to tackle then have a look at this selection: https://github.com/nextcloud/server/issues?q=is%3Aopen+is%3Aissue+label%3A%22good+first+issue%22

[come-nc]

@Keeper-of-the-Keys Thank you for your contribution!
Would you be interested in a guest account on our Nextcloud Talk instance ? It hosts a dev chat for community. I can send an invite to the email you used in the commits if that’s okay with you.