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/assistant_tools/src/project_notifications_tool.rs

@@ -200,7 +200,7 @@ mod tests {
 
         // Run the tool before any changes
         let tool = Arc::new(ProjectNotificationsTool);
-        let provider = Arc::new(FakeLanguageModelProvider);
+        let provider = Arc::new(FakeLanguageModelProvider::default());
         let model: Arc<dyn LanguageModel> = Arc::new(provider.test_model());
         let request = Arc::new(LanguageModelRequest::default());
         let tool_input = json!({});