user: allow setting default group

[joshmoore]

migrate code from openmicroscopy and fix flake8

see: ome/openmicroscopy@8442eed
https://forum.image.sc/t/set-user-default-group-from-command-line/35171

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Adding a parameter to set a user's default group when joining a new group, and a helper function to set the default group for a user.

Ideally the CLI should also allow an ad-hoc "set group" command on it's own, but I see this as an incremental improvement towards that goal, and it certainly answers the use case I have for adding users to a group and setting that to be the default group in one command.

What this PR does

Allows a CLI user to set the default group of a user when adding the user to a group.

Testing this PR

1. required setup

Apply the diff in this PR.

2. actions to perform

Identify a group which your test user does not belong to.

Issue a CLI command with the new --as-default flag like so, with 103 as an example:

omero user joingroup --group-id 103 --as-default

Then issue a further

omero user joingroup --group-id 103

3. expected observations
   Output like the following should appear, if the user was not already a member of the group.

Set the default group of user 793 to group 153

Then

793 is already in group 103

Related reading

Link to cards, tickets, other PRs: https://trello.com/c/sjEk7VQG/487-cli-manage-group-and-user-missing-features

1. background for understanding this PR

2. what this PR assists, fixes, or otherwise affects

The missing ability to set the default group of a user by the CLI.

[joshmoore]

Some thoughts of mine from: ome/openmicroscopy#5914 (comment)

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I don't know if I will have time to make a commit today but on top of this I would imagine the following:

• (possibly) use just the first group listed as the default? (as-default becomes set-default)
• a bin/omero group default [--set] $user [$group] method to get/show the default
• python tests

[joshmoore]

Reopening with pytest fix

[will-moore]

Clearly (as mentioned) it would be useful to set the default group to a group that the user is already a member of. This would allow a regular user to set their own default group, without having to be an Admin, which is required by omero user joingroup
However, this otherwise works as described, so 👍

[joshmoore]

👍 also happy to take PRs and/or suggestions on which of the API improvements to use.

[will-moore]

Looking for PRs that could go in a release soon. I this "done" for now?

[joshmoore]

Tests are missing and there's no final word on what we want the API to be. Feel free to go ahead without it.