Add a way to get failed request details

[code-asher]

All the headers, body, etc, so we can debug more easily. For example we could put it in an editor pane? Then they can copy and paste it to us, if the problem is not immediately obvious.

So for example we could have something like:

Failed to authenticate: some error <click for details>

In a perfect world they could just use the network tab but that does not log requests from extensions.

[EhabY]

With #580, all requests are logged in the Coder output channel. If they have coder.httpClientLogLevel to headers/body then they'll see all the relevant details.