Helm 3: Add new chart version reference system based on Docker

[jdolitsky]

As discussed in Helm 3 repos meeting and on cncf-helm mailing list.
Notes here: https://hackmd.io/6cEbLF6DQlyGtUbsJAKQzg

This is essentially the only breaking change we need to make in order to be able to implement things like #55 behind the scenes post-3.0.0.

The schedule of that project, as well as related things such as helm push, helm login should not affect the Helm 3 schedule as these can be layered in as features in Helm 3.1/3.2/3.3 if necessary.

[stefsuse]

let's do it. will let a maintainer hit the real approval button..

[stefsuse]

what other characters besides '-' are needed? Ex 4.0.0-alpha1
I can't think of a reason why you would want to type for example, helm install stable/chart-~1.0.1 when you know that chart-1.0.1 is stable for your needs. Unless I just totally read this wrong.

[jdolitsky]

@stefsuse take a look at what app registry does in regards to releases vs channels: https://github.com/app-registry/appr/blob/master/Documentation/quick-start.md

By other characters, I mean separators between name and version that are not : (e.g. @ to specify an immutable release)

What comes after the : character is the chart version, and that format will comply with whatever version validation is already in place

[jdolitsky]

Closing this, will open another PR with a general summary of updates needed