bugfix: register workqueue metrics in controller-runtime firstly

[mars1024]

What this PR does / why we need it:
Ref to #1372 , because of importing race as #1372 (comment), workqueue metrics do not work now.
And this PR try to use an import with highest order to fix this.

Which issue(s) this PR fixes:
Fixes #1372

Signed-off-by: Bruce Ma [email protected]

[hectorj2f]

@mars1024 Could you share an example in this PR of what you are getting solved by importing this package ? What were we missing before ?

[mars1024]

Yeah, let's start with the precondition that kubefed is exposing the metrics registry defined in controller-runtime/pkg/metrics.
https://github.com/kubernetes-sigs/kubefed/blob/16b2f5cc4f05c9e9b696970295f353c56d33aa3a/cmd/controller-manager/app/controller-manager.go#L402-L404

So we must make sure that the metrics collectors defined in controller-runtime/pkg/metrics will be used by client-go/util/workqueue through calling SetProvider function to get itself registered, and the SetProvider function has a sync.Once to admit only the first call.

SetProvider is being called in init functions of two packages, k8s.io/component-base/metrics/prometheus/workqueue and sigs.k8s.io/controller-runtime/pkg/metrics, and both of them are imported by kubefed, here is the dependency paths,

kubefed-controller-manager -> k8s.io/apiserver/pkg/server -> k8s.io/apiserver/pkg/storageversion -> k8s.io/component-base/metrics/prometheus/workqueue
kubefed-controller-manager -> sigs.k8s.io/kubefed/cmd/controller-manager/app -> sigs.k8s.io/controller-runtime/pkg/metrics

From the specification of golang, we will know that k8s.io/component-base/metrics/prometheus/workqueue wins, and client-go/util/workqueue will never use the metrics collectors(defined in sigs.k8s.io/controller-runtime/pkg/metrics) which are being exposed.

So this PR is trying to import sigs.k8s.io/controller-runtime/pkg/metrics before k8s.io/component-base/metrics/prometheus/workqueue to make sure calling SetProvider firstly.

[mars1024]

In our product environments, we are using kubfed on dependencies of kubernetes 1.17 which has no k8s.io/apiserver/pkg/storageversion.
So the race condition of SetProvider was missed before.

[mars1024]

/assign @hectorj2f

[hectorj2f]

/lgtm

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