[FEATURE]: Add a textbox to set OpenAI compatible URL for local or remote custom connectors

Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

Currently, the experience of adding a custom (local or remote) OpenAI-compatible connector seems to work as follows:

• Type /connect
• Add a lower case ID for the connector
• Set the API key and press enter

However, this does not enable a working configuration since for openAI comaptible endpoints you need optional provider attributes to be added such as URL and others.

I suggest to enable connectors adding to the connector configuration dialog:

• A combobox or whatever to select OpenAICompatible configuration (or other well known)
• If the OpenAI-compatible option is selected, ask for a baseURL.
• After adding the API key, a test connection button may appear to test the connection at that moment with appropruiate feedback. If the connection test is succesful, a Save button should be enabled with appropriate feedback.

The expected output is to set this configuration automatically as a new connector provider in the corresponding opencode.json configuration file. That would ease the process of configuring instead of having to ask the LLM how to do it and work on a json file which is not a very polished UX experience.

Hope this is useful!