Show progress indicator for more operations, e.g. "discard changes"

**Is your feature request related to a problem? Please describe.**
When pushing and pulling, a progress indicator shows up that lets me know that the keypress has been received and lazygit is working on it.

But there are other operations that can take a longer time, such as rebasing, or "discard all changes" when the file tree is showing.

**Describe the solution you'd like**
Show a progress indicator, similar to the one for push and pull.

**Describe alternatives you've considered**
I wonder whether the indicator would be disruptive in case the operation is fast.

**Additional context**
Add any other context or screenshots about the feature request here.