Support multiple OpenAI compatible providers (#34212)

TODO
- [x] OpenAI Compatible API Icon
- [x] Docs
- [x] Link to docs in OpenAI provider section about configuring OpenAI
API compatible providers

Closes #33992

Related to #30010

Release Notes:

- agent: Add support for adding multiple OpenAI API compatible providers

---------

Co-authored-by: MrSubidubi <dev@bahn.sh>
Co-authored-by: Danilo Leal <daniloleal09@gmail.com>

crates/agent/src/thread.rs

@@ -5490,7 +5490,7 @@ fn main() {{
         let thread = thread_store.update(cx, |store, cx| store.create_thread(cx));
         let context_store = cx.new(|_cx| ContextStore::new(project.downgrade(), None));
 
-        let provider = Arc::new(FakeLanguageModelProvider);
+        let provider = Arc::new(FakeLanguageModelProvider::default());
         let model = provider.test_model();
         let model: Arc<dyn LanguageModel> = Arc::new(model);