Would be nice to have registryMirrors via maven plugin configuration and / or properties like -Djib.from.auth.username

https://github.com/GoogleContainerTools/jib/tree/master/jib-maven-plugin#global-jib-configuration

I try to combine jib-maven-plugin with registry-mirrors in gitlab build / local development.

In this scenario I find the available global-config little bit "unclean".

Maybe something like this improve this:

```

com.google.cloud.tools
jib-maven-plugin


...


....



registry-1.docker.io


gcr.io
mirror.gcr.io


company
cr.company.cloud






```

The with properties similar to -Djib.from.auth.username .. I would like to define the auth stuff:

`-Djib.registryMirror.[id].username and -Djib.registryMirror.[id].password`