Deprecate etcd storage provider

[maiqueb]

I wonder if we should deprecate - and remove - this storage provider.

It is hard to maintain, making removing controller-runtime harder - which in turn makes bumping the k8s API harder.

Is anyone on the community actively using this ?

[maiqueb]

Plan is:

• tag a release from latest master, and create a release branch from it.
• get rid of etcd stuff on latest master.
• backport fixes (not features) to the etcd branch for 90 days.

Please track the deprecation issue for updates.