FEATURE: User workspaces

[nezaniel]

This introduces the concept of user workspaces on a higher level via the workspace provider

Upgrade instructions

none

Review instructions

none

Checklist

• [x] Code follows the PSR-12 coding style
• [] Tests have been created, run and adjusted as needed
• [x] The PR is created against the 9.0 branch
• [ ] Reviewer - PR Title is brief but complete and starts with FEATURE|TASK|BUGFIX
• [ ] Reviewer - The first section explains the change briefly for change-logs
• [ ] Reviewer - Breaking Changes are marked with !!! and have upgrade-instructions