Add character counts plugin

The character counts plugin should:

- [ ] Be able to count characters left to type
- [ ] Let you type past the limit of characters allowed and show which portion of the text is over the limit
- [ ] Allow different ways to count characters according to platform/setting
- [ ] Allow showing multiple ways to count characters at the same time

You can [use the TipTap character counts plugin](https://tiptap.dev/docs/editor/extensions/functionality/character-count) as a base. If it needs rewriting, [you can look directly at the source code](https://github.com/ueberdosis/tiptap/blob/main/packages/extensions/src/character-count/character-count.ts).