Adding a new feature for reward sketching

**Is your feature request related to a problem? Please describe.**
Being able to annotate rewards is missing in this label studio. This reward annotation is useful for training RL agents.

**Describe the solution you'd like**
I'd like to have a way to create reward sketches like done here https://sites.google.com/view/data-driven-robotics/ on video data.

**Describe alternatives you've considered**
I have not seen anything close to this in the repo.

**Additional context**
These reward sketches are useful to have to train RL agents. This is the closest you can get to have a supervised signal for robotics.