Lack of feedback from bad HEAD responses

When watchtower tries to perform a HEAD check for container image updates, if the repository responds with anything but a valid JSON response, the only feedback to the user is a parade error.

It would be much more helpful if the warning would say "failed to parse response, see log for details", and then that the response was logged in full (using notify=no).

The message is a bit cryptic, but what it means is that the repository responds with something that is not valid JSON. Instead of starting with {, it starts with S, which is probably a proxy error. Watchtower still falls back to doing a regular pull though, so I'm not sure what else we can do...

If the message is cryptic and making it difficult to troubleshoot, I wonder if it would be worthwhile investigating a way to make that particular error more verbose (but not run the entire container verbose as that might just cause noise, even more so if it's an intermittent issue (seems to be in my case))?

Originally posted by @modem7 in https://github.com/containrrr/watchtower/issues/1514#issuecomment-1371402612