Show rollout progress in fluxctl release

[squaremo]

As of #1380 and related PRs, flux reports the pod counts (ready, available, etc.) and any conditions indicating a rollout error. It would be great to have an option to fluxctl release watch the rollout happen -- for peace of mind, at the least.

I believe this can be done statelessly -- i.e., you figure out which workloads you need to watch, then call ListControllers for those workloads, and report based on what it says, until all the workloads are in a terminal state (either rolled out, or stuck).

[squaremo]

Hacktoberfest caveat: this is non-trivial, but doesn't need deep knowledge of flux's internals.

[kingdonb]

No further enhancements can land in Flux v1,

• Flux v1 is in maintenance mode #3320