Adds injection metrics for fake pod injection

[atwamahmoud]

What type of PR is this?

/kind feature

What this PR does / why we need it:

Adds metrics for injected pods from PodInjectionPodListProcessor.

Mainly updates unschedulable_pods_count metric with labels injected & skipped_injection for injected pods and pods that were removed due to limit.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?

NONE

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

[k8s-ci-robot]

Hi @atwamahmoud. Thanks for your PR.

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[x13n]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: atwamahmoud, x13n

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