feat: Improved workspace join process

[jo-gross]

Closing issues:

• Closes: feat: Workspace join improvements #104

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Describe your work, what changed

Until now you entered/invited members by sharing the workspace id. Obviously this is not the best way, you had no control about who is joining, ...

With this PR i improved the whole process by adding a JoinRequest list, showing the users who wants to join. Additionally i added random join codes with time and usage limitation options.

Affected sites (please check during review):

• Settings got new list with users who wants to join
• Workspace select page also shows the request list

Further comments

As mentioned in #521 some kind of notification would be awesome, but thats something for the future...