Ignore immutable registry errors when source image changed with a flag or configuration

[R1cc4rd07]

Hi all,

I've encountered an issue uploading images to my immutable registry.

When the source image gets changed for whatever reason dregsy tries reuploading the image but fails because the image tag already exists and can't be overwritten.

Log message:

The image tag '1.20.12' already exists in the 'xxxxxx/kubectl' repository and cannot be overwritten because the repository is immutable.

I think there should be a configuration/flag available to ignore errors like this and simply drop a warning at the end saying something like:

The source image for <insert repo name> was changed in < tag version >. The image was not uploaded because the target registry is immutable.

But this should not be an error just a warning. I suggest a new field for the configuration of dregsy tasks something like this:

"tasks": {
  [
    "source": {
      "regsitry": "my-registry.com",
      "auth": "xxxxxxxxx"
    },
    "target": {
      "registry": "my-traget-registry.com",
      "auth": "xxxxxxxxx",
      "immutable": true
    },
    ...
  ]
}

or simply a flag called "ignoreImmutable" or something like this.

Let me know what you think.