Add sidecars support

[fgiannetti]

Add the ability to specify sidecar containers.
The motivation on this change is because I need to implement a whitelist for the registry (in proxy mode) and as the registry image does not support a whitelist configuration, the alternative is running a reverse proxy in the pod to reject the non-whitelisted images
The reverse proxy could run in other pod, however, allowing sidecars to be set will help whoever needs it.
Hope it helps!

[0xDEC0DE]

This looks promising. A terrific use case for this would be running docker_auth as a sidecar, instead of as a separate pod.

Do you think you could update the docs with instructions on getting that working?

[fgiannetti]

This looks promising. A terrific use case for this would be running docker_auth as a sidecar, instead of as a separate pod.

Do you think you could update the docs with instructions on getting that working?

I modified the Readme file to include this field, but the sidecar container configuration is unique to each one. That configuration should be included using this new 'sidecars' feature ;)