Adjust CLI to support variants of source (inputs) and ai provider

[StefMa]

Since we decided to get rid of support "only" github issues/pr but a variantiy of different sources we have to adjust the CLI to support that soo.

I imagine something like this:

summaraizer SOURCE ARGUMENT AI_PROVIDER --flags

SOURCE
This is a cobra command like github (suport right now), github_pr (#15), gitlab (#11 and #15), or reddit (#16).
Each of those needs an 👇

ARGUMENT
The argument is the argument for the SOURCE. The source needs to know from where it grabs the information.
Examples:
github -> ioki-mobility/summaraizer/15
github_pr -> ioki-mobility/summaraizer/17 (assumption that this is an PR)
gitlab -> (similar to github)
reddit -> r/sub_name/thread_name
...

AI_PROIVDER
The ai provider we support. This can be openai (#3 & #17), ollama (support right now), or mistral (#4).
Those don't need "ARGUMENTS" (but could).

--flags are used to change the "behaviour" of the SOURCE and AI_PROVIDER.
A typical example is the token. ai-token, gitlab-token, github-token...
Also the ai-model and stuff...