Proposal: synchronize cgroupv1 deprecation announcements

[haircommander]

At a breakout session in Container Plumbing Days, @AkihiroSuda brought up the topic of a timeline to the cgroupv1 deprecation and removal. In discussing, we came up with a handful of ideas around it. I will begin by summarizing them. As a note: "we" in this conversation includes maintainers of OCI runtimes, and higher level container managers.

• Do we announce deprecation earlier than distros and the kernel (similar to how systemd did)?
• What are the steps that projects should take in announcing/dropping support
• Do we announce as a group?

There seemed to be consensus on the idea of having the OCI runtimes and managers make some sort of shared announcement on the intention of dropping cgroupv1 support. It doesn't require consensus on all implementations, but I think it would be most impactful if it was done together. Note: this conversation is tangential but related to a similar conversation happening in Kubernetes. in this conversation, we're focusing on lower levels, but the Kubernetes community could take a different timeline if they choose.

@AkihiroSuda suggested we open an issue here to announce follow-up conversations about it. @jberkus created a channel in the OCI slack to discuss further, but I'll let this be an entry point into that conversation. If you know of someone who may be interested in such a conversation, please tag them here or invite them to the slack channel (folks can join the OCI slack by following this link)