Add Word/Character Counter and Limitation

[soranoo]

Is your feature request related to a problem? Please describe.
Some users are always trying to break the service by typing/uploading/embedding tons of nonsense. By adding limitations, hopefully, it can prevent users doing so at the UI level.

Describe the solution you'd like

1. Add a word/character counter to the editor that is only visible in edit mode
2. Add word/character limitation
3. Add upload & embedding limitation
4. Add max block deep
5. Option to remove empty trailing blocks

Bonus
[ ] I'm a sponsor and would appreciate if you could look into this sooner than later 💖