Be able to disable notifications about 503 dockerhub errors

[kerphi]

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

I have a working watchtower configured with WATCHTOWER_POLL_INTERVAL=60 and with slack notification enabled.

Somethimes I noticed the slack notification report some strange errors:

Unable to update container "/qualimarc-watchtower": Error response from daemon: Head "https://registry-1.docker.io/v2/containrrr/watchtower/manifests/1.4.0": received unexpected HTTP status: 503 Service Unavailable. Proceeding to next.

Although I setup watchtower with a low noise this way:

      WATCHTOWER_DEBUG: "false"
      WATCHTOWER_NO_STARTUP_MESSAGE: "true"
      WATCHTOWER_WARN_ON_HEAD_FAILURE: "never"

Describe the solution you'd like

I would expect a new parameter to be able to ignore dockerhub (or registry) errors, or maybe also network errors.
Maybe a such parameter :

WATCHTOWER_WARN_ON_DOCKERREGISTRY_ERROR: "true"

Describe alternatives you've considered

An alternative could be to totally remove notifications about theses errors and just report something in the watchtower logs.

Additional context

No response

[github-actions]

Hi there! 👋🏼 As you're new to this repo, we'd like to suggest that you read our code of conduct as well as our contribution guidelines. Thanks a bunch for opening your first issue! 🙏

[kerphi]

In addition, I could have other similar slack notification errors:

Error response from daemon: Get "https://registry-1.docker.io/v2/": context deadline exceeded (Client.Timeout exceeded while awaiting headers). Proceeding to next.

Error response from daemon: Get "https://registry-1.docker.io/v2/": read tcp 10.34.202.211:48124->44.205.64.79:443: read: connection reset by peer. Proceeding to next.

Error response from daemon: Get "https://registry-1.docker.io/v2/": net/http: request canceled while waiting for connection (Client.Timeout exceeded while awaiting headers). Proceeding to next.

[Niek]

See #1313 (comment)

The only way seems to be to make a separate template.