User Groups: Add ability to manage users directly from the group workspace

[NguyenThuyLan]

Prerequisites

• I have added steps to test this contribution in the description below

If there's an existing issue for this PR then this fixes

Description

• Adds a Users panel to the User Group details workspace view, allowing administrators to add or remove users directly from the group editor — without having to navigate to each user individually.
• The workspace context now loads the current users of the group on open, tracks pending additions/removals client-side, and persists the changes via the Management API on save.
• The changes are properly integrated into the workspace's dirty-state detection (getHasUnpersistedChanges), so the "unsaved changes" guard triggers when users are added or removed.

Test plan

• Open an existing user group — the Users panel should display the current members of the group.
• Add a user to the group and save — the user should be persisted to the group via the API.
• Remove a user from the group and save — the user should be removed via the API.
• Create a new user group with users selected — users should be added after the group is created.

[AndyButland]

I've only given this a quick look-over @NguyenThuyLan, so you have some feedback for the start of your working day. Please see what you think on my comments. I'll try to pull it down for some testing when I'm in tomorrow.

[NguyenThuyLan]

Done, I separated the user list into a separate element, so when adding or removing users from the list, it will be saved instantly

[AndyButland]

Looks great and works correctly @NguyenThuyLan.

I see now that adding or removing users from the list happens immediately - I don't have to press "Save". From the discussions I've seen you've had with @nielslyngsoe , that looks as expected. Longer term I think it would be better if this occurred on "Save" though, as the "Users" list is within the workspace and looks like it should be persisted only when you save.

Comments to consider are mostly around the edge-case of > 100 users in the group.

[AndyButland]

Just one tiny thing then I would say this looks good to me, on the understanding that the intention is to be able to provide a paged list further down the line. It will already meet the need for most projects.

I'll approve but think this needs @nielslyngsoe to look over too before merging.

[NguyenThuyLan]

Thanks @nielslyngsoe ,everything has been updated. Please let me know if anything else is needed

[nielslyngsoe]

Changes look good to me, so please have someone verifying that it works as expected :-)

[AndyButland]

I'll take one further look over from a testing perspective @NguyenThuyLan - than I take it from your comment above @nielslyngsoe that this is OK to merge.

[leekelleher]

@AndyButland I was giving this a quick review, (@NguyenThuyLan asked if I had time). Overall, I'm happy with it, but had the same thoughts as you outlined about the "Save" (#22215 (review)) and pagination (#22215 (review)). If these are going to be address later, then all good.

[AndyButland]

OK, if you've tested it out @leekelleher we can merge this in my view. As I understand we need a bit more plumbing to allow other actions to hook into the "Save" for a workspace before we can support delegating the save to this operation.