Fixed metrics collector aggregation issue for NEG metrics in MT

[priyapande]

To allow providerConfigId to be set for multi-project use-cases, added a new NegMetrics struct that registers to the existing metrics methods so we can use it as an additional label in all our metrics to support per NEG controller metrics.

Meanwhile, fixed the bug by creating a global metrics collector that aggregates the metrics based on NegSyncerKey.

Merge depends on - #2951

[k8s-ci-robot]

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[priyapande]

/assign @swetharepakula @panslava

[k8s-ci-robot]

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[TortillaZHawaii]

/ok-to-test