Add label changes for service-monitor

[chiayi]

This changes service-monitor to match against the "extensions" label when SplitControllerAndExtensions is enabled. \

What type of PR is this?

Uncomment only one /kind <> line, press enter to put that in a new line, and remove leading whitespace from that line:

/kind breaking

/kind bug

/kind cleanup
/kind documentation
/kind feature
/kind hotfix

What this PR does / Why we need it:
This is potential fix for #3190

Which issue(s) this PR fixes:
For #3190

Special notes for your reviewer:

[chiayi]

Currently looking into exactly what metrics we will be missing if we do move the labelmatching.

[agones-bot]

Build Failed 😱

Build Id: 99f1b28a-5162-4c84-823c-5986ffff203f

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[agones-bot]

Build Succeeded 👏

Build Id: 576ad7ea-4b9b-4262-b957-77adfd8e292c

The following development artifacts have been built, and will exist for the next 30 days:

• image: us-docker.pkg.dev/agones-images/ci/agones-controller:1.33.0-d5c2459-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-sdk:1.33.0-d5c2459-linux-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-ping:1.33.0-d5c2459-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-allocator:1.33.0-d5c2459-amd64
• Linux C++ SDK (build): agonessdk-1.33.0-d5c2459-amd64-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.33.0-d5c2459-amd64.zip

A preview of the website (the last 30 builds are retained):

• https://d5c2459-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/googleforgames/agones.git pull/3201/head:pr_3201 && git checkout pr_3201
• helm install agones ./install/helm/agones --namespace agones-system --set agones.image.registry=us-docker.pkg.dev/agones-images/ci --set agones.image.tag=1.33.0-d5c2459-amd64

[markmandel]

Just wanted to check in, see if this needed any additional attention to help move it along.

[google-oss-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: chiayi, zmerlynn
Once this PR has been reviewed and has the lgtm label, please assign markmandel for approval. For more information see the Kubernetes Code Review Process.

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[agones-bot]

Build Succeeded 👏

Build Id: beeae07e-ea2b-41e2-af0a-e31a9020b42c

The following development artifacts have been built, and will exist for the next 30 days:

• image: us-docker.pkg.dev/agones-images/ci/agones-controller:1.33.0-dev-2882677-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-sdk:1.33.0-dev-2882677-linux-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-ping:1.33.0-dev-2882677-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-allocator:1.33.0-dev-2882677-amd64
• Linux C++ SDK (build): agonessdk-1.33.0-dev-2882677-amd64-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.33.0-dev-2882677-amd64.zip

A preview of the website (the last 30 builds are retained):

• https://2882677-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/googleforgames/agones.git pull/3201/head:pr_3201 && git checkout pr_3201
• helm install agones ./install/helm/agones --namespace agones-system --set agones.image.registry=us-docker.pkg.dev/agones-images/ci --set agones.image.tag=1.33.0-dev-2882677-amd64

[agones-bot]

Build Failed 😱

Build Id: de895adf-16de-443c-9073-b65501ef2c46

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• Cloud Build log download

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