Tune release-blocking kind job resources down

[spiffxp]

The kind release-blocking prowjobs have been ending up in error
state over the past few week days, often due to pods being unable
to schedule due to insufficient CPU. We've been seeing increased
PR traffic due to v1.19 getting released, and a concerted attempt
to clear the backlog of v1.20 PRs that were waiting for code thaw.

The kind release-blocking jobs were the only jobs migrated to
k8s-infra-prow-build that reserved 7300m CPU. The next highest
cpu limit is 7, used by the verify presubmit and bazel-test periodic
jobs. These jobs have not been ending up in error state.

I was originally going to match the kind presubmit jobs, which use
4 cpu, but they have been failing a lot today during times I would
correlate with high PR volume. I'm still tuning the memory to match
based on graphs in the issue linked to this PR.

Hoping to address #19080

[spiffxp]

/cc @BenTheElder
FYI @kubernetes/ci-signal

[hasheddan]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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[k8s-ci-robot]

@spiffxp: Updated the job-config configmap in namespace default at cluster default using the following files:

• key kind-release-blocking.yaml using file config/jobs/kubernetes-sigs/kind/kind-release-blocking.yaml
• key 1.16.yaml using file config/jobs/kubernetes/sig-release/release-branch-jobs/1.16.yaml
• key 1.17.yaml using file config/jobs/kubernetes/sig-release/release-branch-jobs/1.17.yaml
• key 1.18.yaml using file config/jobs/kubernetes/sig-release/release-branch-jobs/1.18.yaml
• key 1.19.yaml using file config/jobs/kubernetes/sig-release/release-branch-jobs/1.19.yaml

In response to this:

The kind release-blocking prowjobs have been ending up in error
state over the past few week days, often due to pods being unable
to schedule due to insufficient CPU. We've been seeing increased
PR traffic due to v1.19 getting released, and a concerted attempt
to clear the backlog of v1.20 PRs that were waiting for code thaw.

The kind release-blocking jobs were the only jobs migrated to
k8s-infra-prow-build that reserved 7300m CPU. The next highest
cpu limit is 7, used by the verify presubmit and bazel-test periodic
jobs. These jobs have not been ending up in error state.

I was originally going to match the kind presubmit jobs, which use
4 cpu, but they have been failing a lot today during times I would
correlate with high PR volume. I'm still tuning the memory to match
based on graphs in the issue linked to this PR.

Hoping to address #19080

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