Custom Chat-Character Support

[TheMasterFX]

Is your feature request related to a problem? Please describe.
We already have the possibility to add custom prompts (/custom-prompt). Which is a nice feature since the user can jump to the variables via tab-key. However the system-prompt is untouched.
To vary the system-prompt we have to use the Modelfiles or the user has to change it every time. Modelfiles are also a great feature, but it has the disadvantage that it is tied to a dedicated language model.

Describe the solution you'd like
It would be nice to define a "Character Template" which can be used on any model and has the possibility to overwrite the systempromt (since as far as I know) has a higher weight than anything which comes after.

Describe alternatives you've considered
Maybe a Solution like text-generation-webui might be a great solution. So non-Admin-Users are able to create and share characters (not only online) but also in an offline company intranet

[tjbck]

Related #665, Let's continue our discussion there.+