Add the ability to tag each todo, both while being created, and after it's already been created

[kresimir-coko]

User should have the option to add a custom tag to each todo. Investigate how best to allow the user to add these tags - maybe by typing a # followed by the tag, or as an option when editing the todo, etc.

Inspiration:

[Rinakat225]

Done on commit: https://github.com/Rinakat225/Todo-list/commit/c4a86ab189383e2ce9db44ab31037d01fa30d37f