Kaniko: Add ability to push to on-premise registries

[IlyaPokamestov]

I've tried to install Kamel on my on-premise Kubernetes cluster with custom docker registry using next command:
kamel install -n kamel --registry=my.registry.com --registry-secret=regcred

Registry secret was created using Kubernetes guid: https://kubernetes.io/docs/tasks/configure-pod-container/pull-image-private-registry/

It's obviously lead to registry connection error, because "registry-secret" parameter requires GKE service account json key as described here: https://github.com/GoogleContainerTools/kaniko#kubernetes-secret

In the logs I can see:

MacBook-Pro:kamel darioswain$ kubectl logs camel-k-jvm -n kamel
INFO[0000] Downloading base image fabric8/s2i-java:3.0-java8 
2019/04/13 21:51:29 No matching credentials were found, falling back on anonymous
INFO[0006] Found sha256:9ac5acb3aa8e7e179eb1fd28cda7dac22ef7deac24f00b50cee56265fa259141 in local cache 
INFO[0006] Executing 0 build triggers                   
INFO[0007] Using files from context: [/workspace/builder-966534887/package/context] 
INFO[0007] Taking snapshot of full filesystem...        
INFO[0008] Skipping paths under /kaniko, as it is a whitelisted directory 
INFO[0008] Skipping paths under /var/run, as it is a whitelisted directory 
INFO[0008] Skipping paths under /secret, as it is a whitelisted directory 
INFO[0008] Skipping paths under /proc, as it is a whitelisted directory 
INFO[0008] Skipping paths under /sys, as it is a whitelisted directory 
INFO[0008] Skipping paths under /dev, as it is a whitelisted directory 
INFO[0008] Skipping paths under /workspace, as it is a whitelisted directory 
INFO[0008] Using files from context: [/workspace/builder-966534887/package/context] 
INFO[0008] ADD . /deployments                           
INFO[0008] Taking snapshot of files...                  
error pushing image: failed to push to destination my.registry.com/kamel/camel-k-jvm:8536073: no token in bearer response:
{"error":"You need to sign in or sign up before continuing."}

I've just firstly found this project and definitely may have a wrong understanding. But I can't find possibility how I can use custom docker registry as described in the Kaniko docs here: https://github.com/GoogleContainerTools/kaniko#pushing-to-different-registries
Kaniko allows to provide custom docker config.json via Kubernetes config map with custom auths.

I will be very appreciated if someone knows how to deal with custom registries or can share any kind of workarounds how to setup them.

BTW: I've opened a PR with possible solution based on the Kaniko Doc: #614, but I'm not a Go expert and need an assistance with it, in case when PR direction is right.