[Feat]: a "no SSL" configuration

### Is your feature request related to a problem? Please describe.

I'm querying a A2A endpoint with http:// (no SSL, as it's a non prod deployment), but it seems it is not supported, or did I miss it?

Right now, the UI displays:
```
Error: An internal server error occurred: HTTP Error 503: Network communication error fetching agent card from https://localhost:5601/api/agent_builder/a2a/docs-agent.json: [SSL: WRONG_VERSION_NUMBER] wrong version number (_ssl.c:1028)
```

I'm getting this log:
```
[BACKEND] 2025-11-26 14:54:30,463 - app - ERROR - An internal server error occurred
[BACKEND] Traceback (most recent call last):
[BACKEND] File "/Users/vincent/installs/agent-builder-demo/a2a-inspector/.venv/lib/python3.13/site-packages/httpx/_transports/default.py", line 101, in map_httpcore_exceptions
[BACKEND] yield
[BACKEND] File "/Users/vincent/installs/agent-builder-demo/a2a-inspector/.venv/lib/python3.13/site-packages/httpx/_transports/default.py", line 394, in handle_async_request
[BACKEND] resp = await self._pool.handle_async_request(req)
[BACKEND] ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[BACKEND] File "/Users/vincent/installs/agent-builder-demo/a2a-inspector/.venv/lib/python3.13/site-packages/httpcore/_async/connection_pool.py", line 256, in handle_async_request
[BACKEND] raise exc from None
[BACKEND] File "/Users/vincent/installs/agent-builder-demo/a2a-inspector/.venv/lib/python3.13/site-packages/httpcore/_async/connection_pool.py", line 236, in handle_async_request
[BACKEND] response = await connection.handle_async_request(
[BACKEND] ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[BACKEND] pool_request.request
[BACKEND] ^^^^^^^^^^^^^^^^^^^^
[BACKEND] )
[BACKEND] ^
[BACKEND] File "/Users/vincent/installs/agent-builder-demo/a2a-inspector/.venv/lib/python3.13/site-packages/httpcore/_async/connection.py", line 101, in handle_async_request
[BACKEND] raise exc
[BACKEND] File "/Users/vincent/installs/agent-builder-demo/a2a-inspector/.venv/lib/python3.13/site-packages/httpcore/_async/connection.py", line 78, in handle_async_request
[BACKEND] stream = await self._connect(request)
[BACKEND] ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[BACKEND] File "/Users/vincent/installs/agent-builder-demo/a2a-inspector/.venv/lib/python3.13/site-packages/httpcore/_async/connection.py", line 156, in _connect
[BACKEND] stream = await stream.start_tls(**kwargs)
[BACKEND] ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[BACKEND] File "/Users/vincent/installs/agent-builder-demo/a2a-inspector/.venv/lib/python3.13/site-packages/httpcore/_backends/anyio.py", line 67, in start_tls
[BACKEND] with map_exceptions(exc_map):
[BACKEND] ~~~~~~~~~~~~~~^^^^^^^^^
[BACKEND] File "/Library/Frameworks/Python.framework/Versions/3.13/lib/python3.13/contextlib.py", line 162, in __exit__
[BACKEND] self.gen.throw(value)
[BACKEND] ~~~~~~~~~~~~~~^^^^^^^
[BACKEND] File "/Users/vincent/installs/agent-builder-demo/a2a-inspector/.venv/lib/python3.13/site-packages/httpcore/_exceptions.py", line 14, in map_exceptions
[BACKEND] raise to_exc(exc) from exc
[BACKEND] httpcore.ConnectError: [SSL: WRONG_VERSION_NUMBER] wrong version number (_ssl.c:1028)
```

### Describe the solution you'd like

Have a config flag to enable https

### Describe alternatives you've considered

_No response_

### Additional context

_No response_

### Code of Conduct

- [x] I agree to follow this project's Code of Conduct