Add AWS ECR support

[chicocvenancio]

Starting the PR, I'll push a few more commits before it is ready for review.

FIX #705

[betatim]

Conflicts need resolving and the test failures checking out. I restarted the build and it failed again so I think this might be a real failure.

Is there a way to avoid having to expand the RBAC rights? If we can avoid giving more permissions that would be a "good thing (tm)". So I thought I'd raise it to see what we can come up with.

What does it mean for people upgrading if we change the RBAC permissions? I have a vague memory that there is a difference between creating and editing permission.

[chicocvenancio]

I'll try to make the config more robust, at this point it is expecting AWS specific config to be there, and since it is not for the CI tests it is failing.

Is there a way to avoid having to expand the RBAC rights? If we can avoid giving more permissions that would be a "good thing (tm)". So I thought I'd raise it to see what we can come up with.
I can't think of a straightforward way of dropping added rights entirely. ECR login tokens expire in 12 hours, right now the tokens are set both in DockerRegistry.password and as a secret binder-push-secret, both need to be set for pushing and pulling images to work. One option to restrict RBAC a little further is to specify the binder-push-secret in the rule, so it only applies to it.

What does it mean for people upgrading if we change the RBAC permissions? I have a vague memory that there is a difference between creating and editing permission.
We're using Pulumi to deploy Binderhub, so I'm not completely sure if helm+tiller does something weird here. I wouldn't expect it to, but I can take a look and test it out.

[ivan-gomes]

@chicocvenancio anything I can help with to get this to the finish line?

[meeseeksmachine]

This pull request has been mentioned on Jupyter Community Forum. There might be relevant details there:

https://discourse.jupyter.org/t/binder-jupyterhub-activity-round-up-week-1/2704/1

[consideRatio]

Hey @chicocvenancio, @ivan-gomes and @betatim! I'm going through various PRs hoping to help them resolve one way or another or perhaps get an updated description about the current status of things.

I'm closing this in favor of the PR building on this with additional commits: #1055.