API way for Ollama to serve a UI

### What are you trying to do? A huge problem with usability right now is that we can not let users enjoy browser based UIs from the box. There is the CORS protection that can not be removed and it blocks browser UIs opened from a local file. The CORS can not be removed (set to *), as then malicious websites could potentially exploit the local Ollama, as the opened page of a bad website could just access local Ollama service. To work-around this, right now we have to recommend installing a reverse proxy which is an overkill for simple users, especially windows ones who just want to have fun and the term "web-server" is associated with something complicated, huge and providing everyone access to your computer. We can recommend them to set Origin to a certain web-site where our UI is hosted, but then users do not feel safe as they *believe* or *feel* the web-page is remote and it can "eavesdrop" their chats. Also, it means they can't open UI locally, they need internet to chat, which goes against the whole idea of a local service. ### How should we solve this? A very easy and logical solution would be to add to existing API a function to serve an "index.html" file. We can add a special optional env header with a path to that single file. Then Ollama could just send its content on the request of "http:/127.0.0.1:11434/index.html" And that's basically it. The CORS protection would be kept and it's very simple to implement. For default installations nothing would change at all but for people wanting to try some browser based UI it would be enough to set the env variable or some "--index=" option at start. Serving folders could theoretically be better but it's already much harder in terms of various security issues and to be honest not really needed as the web page can load other resources it needs from remote web-sites, like github.io or whatever. ### What is the impact of not solving this? A lot of simple users are forced to either drop CORS protection or just drop th…