Shortcuts for relation LABELS

**Is your feature request related to a problem? Please describe.**
Labeling relations currently requires several clicks:
- click on first region
- click on "create relation" in sidebar (This can be already done with Alt+R)
- click on second region
- click on "..." in relations
- click on labels textbar
- click on desired label

**Describe the solution you'd like**
Could you add keyboard shortcuts for selection relation LABELS? I'm thinking of something like:
- "R" and "1" = select first relation label
- click on first region
- click on second region

**Describe alternatives you've considered**
I've seen https://labelstud.io/guide/labeling.html#Customize-hotkeys , but don't think it offers this feature yet. Please correct me if I'm wrong.

**Additional context**
Using label studio 1.4.0. Thanks for this great tool!