Support relocating to an insecure registry

[bryanl]

The project does not appear to have the ability to relocate an image to an insecure registry. This functionality would be useful when working with local registries and not having to worry about TLS.

[glyn]

Please could you provide some steps to reproduce the issue.

This worked fine for example:

$ docker run -d -p 5000:5000 --restart=always --name registry registry:2
$ ./irel copy nginx localhost:5000/nginx --skip-tls-verify
copied docker.io/library/nginx to localhost:5000/nginx with content digest sha256:2539d4344dd18e1df02be842ffc435f8e1f699cfc55516e2cf2cb16b7a9aea0b