Reduce memory usage by scoping informers

[youngbo89]

What type of PR is this?

/kind bug

What this PR does / why we need it:

This PR reduces the memory usage of vpa-updater and vpa-admission-controller in large clusters by scoping informers to namespaces.

Test Results

Cluster-Info:

$ k get pod --all-namespaces | wc -l
    8915
$ k get ds --all-namespaces | wc -l
      17
$ k get deploy --all-namespaces | wc -l
    6316
$ k get sts --all-namespaces | wc -l
      20
$ k get rs --all-namespaces | wc -l
   63861
$ k get job --all-namespaces | wc -l
      87

Running arguments:

      spec:
        containers:
        - args:
          - --vpa-object-namespace=my-namespace
          env:
          image: autoscaling/vpa-admission-controller:1.0.0 # or patched one
---
      spec:
        containers:
        - args:
          - --vpa-object-namespace=my-namespace
          image: autoscaling/vpa-updater:1.0.0 # or patched one

Image:1.0.0

NAME                                                             CPU(cores)   MEMORY(bytes)
vpa-admission-controller-youngbo-6595d7855c-tc2n8                6m           2348Mi
vpa-recommender-84d65bf78c-lr64k                                 3m           83Mi
vpa-updater-youngbo-74f7584cb6-z8dzm                             1m           3899Mi

Image:1.0.0-patched:

NAME                                                             CPU(cores)   MEMORY(bytes)
vpa-admission-controller-youngbo-8566bbd869-wqppr                2m           14Mi
vpa-recommender-84d65bf78c-lr64k                                 9m           82Mi
vpa-updater-youngbo-5f56bf954b-sgzx8                             1m           42Mi

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?

- vpa-updater: Reduce memory usage when --vpa-object-namespace option provided
- vpa-admission-controller: Reduce memory usage when --vpa-object-namespace option provided

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

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: youngbo89
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• vertical-pod-autoscaler/OWNERS

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[k8s-ci-robot]

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[adrianmoisey]

This is awesome!

[raywainman]

Nice optimization!

/ok-to-test

[raywainman]

/lgtm

[kwiesmueller]

Can you add tests that confirm this works as intended e2e?