update continuous performance test jobs

[ReToCode]

What this PR does, why we need it

• With Update performance tests serving#14289 merged, this updates the performance test jobs
• Drops the old mako/kperf jobs
• Adds a new job calling the new script

[ReToCode]

/assign @upodroid
/assign @dprotaso

[dprotaso]

/lgtm
/approve

[knative-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: dprotaso, ReToCode

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[knative-prow]

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

• key serving-main.gen.yaml using file prow/jobs/generated/knative/serving-main.gen.yaml

In response to this:

What this PR does, why we need it

• With Update performance tests serving#14289 merged, this updates the performance test jobs
• Drops the old mako/kperf jobs
• Adds a new job calling the new script

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