[Platform][OpenRouter] Add EU routing support and user model selection

[lochmueller]

Q	A
Bug fix?	no
New feature?	yes
Docs?	yes
Issues
License	MIT

The Branch will add two OpenRouter features:

• Enable EU routing via enum in the ModelApiCatalog and PlatformFactory to use the EU route internally
• Support user defined models via separated Endpoint in ModelApiCatalog to reduce
• Add an example that use both features

[lochmueller]

@OskarStark I create a fresh PR for my changes.

The one Fabbot test that failed is a false positive.
It suggests Vector instead of Vektor for the store bridge.
But the bridge is actually called Vektor.

[chr-hertel]

is there an easy way to test another region - somehow i can't just directly find it and my key gets me a 401 here. any hint?

[lochmueller]

Documentation describe it like "you have to contact the sales team to get access to the EU only routing". I have the same problem like you and I add the code to be Opernrouter-feature complete (more or less)