feat: Allow kubernetes workload scaler to query additional namespaces

[nmische]

This PR is related to #7310. It updates the kubernetes workload scaler such that additional namespaces beyond the scaled object's namespace may be queried for pod counts.

This update proposed in this PR:

• Is backwards compatible
  • If no namespace is defined in the trigger spec the scaled object's namespace is used for the pod list operatation
• Allows querying a different namespace by setting namespace to an alternate namespace
• Allows querying all namespaces by setting namespace to *
• Adds pagination to the kubernetes API call to prevent the scaler from consuming too many resources

Checklist

• When introducing a new scaler, I agree with the scaling governance policy
• I have verified that my change is according to the deprecations & breaking changes policy
• Tests have been added
• Ensure make generate-scalers-schema has been run to update any outdated generated files.
• Changelog has been updated and is aligned with our changelog requirements
• A PR is opened to update our Helm chart (repo) (if applicable, ie. when deployment manifests are modified)
• A PR is opened to update the documentation on (repo) (if applicable)
• Commits are signed with Developer Certificate of Origin (DCO - learn more)

Fixes #

Relates to #7310

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[github-actions]

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