VPA: fixed flags script to include constants values

[omerap12]

What type of PR is this?

/kind cleanup

What this PR does / why we need it:

This PR improves the VPA flag documentation generator script introduced in #7618. Previously, when flags had default values defined as constants (e.g., DefaultOOMBumpUpRatio), the script would output 0 as the default value in the generated documentation. For example:

DefaultOOMBumpUpRatio float64 = 1.2 // Memory is increased by 20% after an OOMKill.

Would result in showing 0 as the default value instead of the actual constant reference.
This PR modifies the script to display the constant reference (e.g., model.DefaultMemoryAggregationInterval) in the documentation rather than 0.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?

NONE

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

NONE

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: omerap12
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[omerap12]

cc @adrianmoisey