Bug fix: Initialize RequestReceivedTimestamp

[liu-cong]

See the difference of the e2e request latency after this fix. Before the e2e latency was showing 1 hour (the max bucket)

[k8s-ci-robot]

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[kfswain]

/lgtm

[ahg-g]

is this marked WIP intentionally?

[liu-cong]

I haven't tested it thus still WIP

[liu-cong]

/unhold

[ahg-g]

/approve

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ahg-g, liu-cong

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