[experimental]: instrument etcd request/response object sizes

[jpbetz]

Experimentally adding metrics and logging of etcd object sizes in requests and responses, broken out by operation and k8s type.

Using this in the short term to inspect server side apply performance.

/kind feature

TODO

[apelisse]

The tests have run, how do you plan on looking at these results?

[apelisse]

Also, to trigger the actual thing that we want to test, we have to apply the following diff:
https://github.com/kubernetes/kubernetes/pull/84870/files#diff-438c18fccd3899026928547522f80743

[apelisse]

You also needs something like this to make sure that SSA is enabled on all requests:

diff --git a/staging/src/k8s.io/apiserver/pkg/endpoints/handlers/fieldmanager/fieldmanager.go b/staging/src/k8s.io/apiserver/pkg/endpoints/handlers/fieldmanager/fieldmanager.go
index 3f2b08984ea..a670ee053a9 100644
--- a/staging/src/k8s.io/apiserver/pkg/endpoints/handlers/fieldmanager/fieldmanager.go
+++ b/staging/src/k8s.io/apiserver/pkg/endpoints/handlers/fieldmanager/fieldmanager.go
@@ -92,7 +92,7 @@ func newDefaultFieldManager(f Manager, objectCreater runtime.ObjectCreater, kind
        f = NewStripMetaManager(f)
        f = NewBuildManagerInfoManager(f, kind.GroupVersion())
        f = NewCapManagersManager(f, DefaultMaxUpdateManagers)
-       f = NewSkipNonAppliedManager(f, objectCreater, kind)
+       //      f = NewSkipNonAppliedManager(f, objectCreater, kind)
        return NewFieldManager(f)
 }

OK, I actually said that actually :-)

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[k8s-ci-robot]

@jpbetz: The following test failed, say /retest to rerun them all:

Test name	Commit	Details	Rerun command
pull-kubernetes-verify	baacaea	link	/test pull-kubernetes-verify

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