feat: Use modelfiles with external API instead of ollama

[keriati]

With this change a modelfile from the ollama hub can be imported in a way that it uses an external model from openAI compatible API instead of ollama.

A pre requirement is to provide an API key and refresh the page so the models are loaded.

In my testing to achieve this we have to copy an existing model's name to two places:

• the Tag name
• the FROM part of the content

This works in my local instance.

I am rather not so sure about this changes as I never touched svelte before.

Probably a checkbox called: use external and a dropdown list to select from external models would be a more complete solution.

Should relate to #665

[explorigin]

I haven't reviewed the frontend code enough to have an opinion on the correctness of this, but I posted some thoughts as to why we should probably do this whole thing differently in the related issue.

[tjbck]

I agree with @explorigin, we might want to have our own "modelfile" format that's extensible and compatible with other LLM runners. I'll close this for now, let's continue our discussion here: #665

[spammenotinoz]

Can we please revisit merging this PR, it works really well.