Server: Flow: Allow creating tags from within the tag selector

[nickvergessen]

1. Go to the workflow UI
2. Create a tag
3. Try to create an access control with that tag :boom:

The problem is that list of tags is cached, but also not updated when a new tag is created.

cc @juliushaertl @blizzz

[juliushaertl]

@jancborchardt proposed to move tagging to general settings (will be done with #17997) but yes, we should still try a search if no tags were found or maybe allow creating new ones right from within the tag picker.

[blizzz]

+1 for creating them, less friction and it is right there where you need it