Is your feature request related to a problem? Please describe.
I know that the world is dominated by OpenAI and Llama models, however there are other existing providers as well like VertexAI.
It would be nice to have a support for it as well.

Describe the solution you'd like
I would like to add a feature more or less working like OpenAI support right now.

Describe alternatives you've considered
None

Additional context
I've already created a PR for this change: open-webui/open-webui#846 . Feel free to comment and change it.