WIP: add option to expand and collapse all children of segment group

[knollengewaechs]

Dev instance

https://collapseallsegmentgroupchildren.webknossos.xyz/

Steps to test:

• go to segments tab in any annotation
• click some segments and create some groups, groups should be nested for at least three levels
• right click any group to access group context menu
• if the segment group has any subgroups, there should be one or two new items: "expand/collapse all subgroups".
• if the group is expanded and some subgroups are expanded and some are collapsed, both entries should be shown
• if the group itself is expanded and all subgroups are collapsed, you should only be able to expand them. the opposite is true if all subgroups are expanded.
• if the group itself is collapsed, you should only be able to expand all subgroups. the group itself will be expanded aswell.

TODOs:

• [x] icon
• [x] switch label
• [x] default: all expanded
• [x] recursively expand subgroups

Issues:

• fixes #7829

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(Please delete unneeded items, merge only when none are left open)

• [x] Updated changelog
• [ ] Updated migration guide if applicable
• [ ] Updated documentation if applicable
• [ ] Adapted wk-libs python client if relevant API parts change
• [ ] Removed dev-only changes like prints and application.conf edits
• [ ] Considered common edge cases
• [ ] Needs datastore update after deployment