Default registry value is not used during docker push

[ravipal]

The registries lists shows an option to set a default registry as shown below. I set "MainACR" as default.

Then during "Docker Images: Push" again I got the below prompt to save mainacr as default registry.

[philliphoff]

The problem is that the extension does not check whether a default already exists before prompting to save a tagged image prefix as the default.