More HTTP-API Endpoints/Arguments to allow more control

[deutsch-thomas]

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

The HTTP-API Endpoint offers too little customizations and lacks a concise response body. When i call the Endpoint, i don't know if an update happend or not.

Describe the solution you'd like

As a User, I want to be able to call an HTTP Endpoint e.g. (curl -H "Authorization: Bearer mytoken" localhost:8080/v1/check-for-update -i or curl -H "Authorization: Bearer mytoken" localhost:8080/v1/update?only-check=true -i) which returns a response whether an update is available or not. However the new docker image is not immediatly pulled and the container is not restartet.

Ideally, there would be another Endpoint, which pulls the new image, but does not restart the container. It would prepare for a very quick installation.

Describe alternatives you've considered

1. carrying the version information in my own images, make the check myself and only use watchtower to pull and restart once i know updates are available
2. have several watchtower instances running with different limitations (one does not update) and try to get the information this way - even if I would achieve my result this way, it would take too many unnecessary ressources on my IoT Device

Additional context

I am using watchtower in an environment, where I want to have as little as possible downtime which has to be planned. Hence, I can't run the update job on a cron cycle or just call the HTTP-API and hope it won't take forever to pull all images and restart the containers one after another.
I have a Web-Application from which i want to request if updates are available and show a notification to my enduser. This user can then decide at which point of time it would be good to update. Ideally, the images are already downloaded by then and only the restarts of all dockercontainers are executed.

[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! 🙏