[Feat]: Character Sheet Support

[TheElo]

Description
I would like to be able to create characters and be able to select them to help me with specific tasks like programming.

Use Case
Currently I have to explain at the begin or ad-hoc while chatting how the LLM should respond, which ads repetition if a certain behavior is expected in more than one chat. By creating, editing and the ability to select a character (and set it as default, together with the default LLM feature request) the usage would be more streamlined.