[receiver/kubeletstats] Move `receiver.kubeletstats.enableCPUUsageMetrics` feature gate to Beta

[odubajDT]

Component(s)

receiver/kubeletstats

Describe the issue you're reporting

Since receiver.kubeletstats.enableCPUUsageMetrics feature gate was introduced in v0.110.0, it should be possible to move it to beta state and have the feature gate enabled by default from the following version.

According to the specification, 2 versions should be enough to be eligible for moving the the next stage. For the current use-case, we would be already on ~15 versions.

[github-actions]

Pinging code owners:

• receiver/kubeletstats: @dmitryax @TylerHelmuth @ChrsMark

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