feat: add support for CSI volumes

[mwritescode]

Fixes #11069

Description

This feature introduces support for Container Storage Interface (CSI) volumes in Knative Serving, enabling users to integrate with a wide variety of storage solutions through the Kubernetes CSI standard. This enhancement allows Knative services to leverage enterprise storage systems, cloud provider volumes, and other storage implementations that support the CSI specification, while maintaining Knative's serverless principles.

Proposed Changes

• Add support for CSI volume type in Knative Serving
• Enable users to mount CSI volumes into their Knative service containers
• Update relevant documentation and examples to include usage of CSI volumes
• Add feature flag control for CSI volume support

Release Note

Adding support for CSI (Container Storage Interface) volumes. This feature allows users to mount CSI-compatible storage volumes into their Knative service containers. It enables integration with enterprise storage solutions and cloud provider storage services that implement the CSI specification. The feature is behind the flag `kubernetes.podspec-volumes-csi`.

[linux-foundation-easycla]

• ✅login: mwritescode / (3380251)

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[knative-prow]

Welcome @mwritescode! It looks like this is your first PR to knative/serving 🎉

[knative-prow]

Hi @mwritescode. Thanks for your PR.

I'm waiting for a knative member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[knative-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: mwritescode
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[dsimansk]

/ok-to-test

[knative-prow]

@mwritescode: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
unit-tests_serving_main	3380251	link	true	/test unit-tests
build-tests_serving_main	3380251	link	true	/test build-tests

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[dsimansk]

@mwritescode could you pls take a look literals syntax in tests?

[dsimansk]

@dprotaso @skonto what's your opinion on adding the support? Personally, I'd like to see a bit of e2e test coverage to confirm and ensure it's supportable from our point of view.