Add restart utility function.

[vifino]

This PR adds the restart(name) function on Api<K> where K is one of Deployment, DaemonSet, StatefulSet or ReplicaSet.
It also adds the complementary method to the kube crate.

To implement this functionality, I chose to add chrono to the kube-core crate, as the alternatives involved lots of code and it's already used in the bigger crate.

This fixes #630 by implementing the necessary functionality.

I hope this PR is acceptable.
Thank you.

[clux]

Hello again! Thanks a lot for doing this.
I think this looks perfectly appropriate! Started CI.

Just a bit of double checking here. I was cross-referencing a bit with kubectl it does seem like they use a fieldManager with a strategic merge patch.

Now, I don't know why they have chosen to do this (it could be a fairly arbitrary choice), but it would be good to make sure that the strategy we use won't interfere with other annotations, so if you are able to double check that (in a quick test with restart on a deploy with more labels to see that other labels persist), that would be great.

[vifino]

Hey @clux!

I've tested this on a few deployments, all work fine. Some of those deployments have lots of labels and quite a few annotations.
A kubectl rollout restart still works just fine after doing it this way.

The only thing I noticed was that there is both a kubectl.kubernetes.io/restartedAt and a kube.kubernetes.io/restartedAt annotation, but that makes sense.
It works just fine for me.

[vifino]

Hm. The rustfmt check fails, but cargo fmt --all does nothing?
I'll apply the changes and force-push.

[clux]

Hm. The rustfmt check fails, but cargo fmt --all does nothing?
I'll apply the changes and force-push.

Ah, sorry, yeah, we use a couple of nightly only formatting rules. make fmt does the equivalent of CI.

[clux]

n a few deployments, all work fine. Some of those deployments have lots of labels and quite a few annotations.
A kubectl rollout restart still works just fine after doing it this way.

Ah, perfect. That's the type of thing I was worried about. (I imagine it would not be like that if we took kubectl's label since they have a manager, but that's irrelevant).

[clux]

Ah, for some reason I have to keep approving since you're a first time contributor. Anyway, if just rustfmt fails here I'll just merge it. There's a follow-up system that fixes any issues.

[clux]

Ah, it's fixed. Perfect. Thank you very much. I'll get it into the next release probably sometime this week :-)

[vifino]

Nice! Thanks for merging.
I'll be glad when the next release gets tagged! :)

[clux]

Released in 0.61.0. Thanks again :-)

[vifino]

Woohoo!