Support for registry proxy configuration

[ucrk]

Is your feature request related to a problem? Please describe.
We need to pull images from a registry which is behind a proxy.
Unfortunately it seems not to be possible to configure a proxy for this use-case yet.

I tried to add the proxy env vars within the deployment manifest of the image-updater but the connection to the registry still fails.

Describe the solution you'd like
It would be great, if it's possible to configure a proxy for the registries within argocd-image-updater-config or globaly with some env vars in the deployment manifest of the image-updater.

[jannfis]

Support for leveraging HTTP_PROXY and related environment has already been implemented by #300, but is not yet released (will be part of upcoming v0.12, but there's no ETA yet)

I agree that a per-repository configuration could come in handy

[ucrk]

thanks!