Cody: Handle network error disconnection

[deepak2431]

When there's any network error during the chat session, it shows unexpected error.

Expected behaviour:

1. If there's a network error when users load the extension and have a valid token. Add an error message that "Could not load Cody due to network error" with a reload button to attempt when the connection is back.
2. If a network error happens during the chat, stop the execution and show an error message in the web view "Network error occurred; try after some time".

[jdorfman]

Thanks @deepak2431

Any changes since you first reported it?

[deepak2431]

@jdorfman I reproduced this again. No changes so far. The issue is the same. I will attach my PR to this issue soon.