add new prow target for performance tests

[ReToCode]

Which issue(s) this PR fixes:
Belongs to knative/serving#14289, detail: knative/serving#14289 (comment)

What this PR does, why we need it:

• Adds a new prow job to run performance tests without mako or kperf.

Additional Notes

• continuous target will be added later (when Update performance tests serving#14289 is merged)
• mako + kperf targets will be dropped later (when Update performance tests serving#14289 is merged and tests are stable)

[ReToCode]

/cc @skonto , @dprotaso

/assign @upodroid

[upodroid]

LGTM

[knative-prow]

[APPROVALNOTIFIER] This PR is APPROVED

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

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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:

Which issue(s) this PR fixes:
Belongs to knative/serving#14289, detail: knative/serving#14289 (comment)

What this PR does, why we need it:

• Adds a new prow job to run performance tests without mako or kperf.

Additional Notes

• continuous target will be added later (when Update performance tests serving#14289 is merged)
• mako + kperf targets will be dropped later (when Update performance tests serving#14289 is merged and tests are stable)

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