fix(mediapackagev2): cdnAuth on OriginEndpoint now generates the required policy

[jamiepmullan]

Issue # (if applicable)

Closes #.

Reason for this change

Description of changes

Setting cdnAuth on OriginEndpoint previously stored the configuration but
did not by itself produce a working endpoint policy — the
CdnAuthConfiguration block on OriginEndpointPolicy is non-functional
without an accompanying gating policy statement that requires the matching
mediapackagev2:RequestHasMatchingCdnAuthHeader condition. Per the AWS docs
[1], both the gating statement and the configuration block are required.

This change:

• Auto-emits the AWS-documented gating policy statement when cdnAuth is set
  on OriginEndpointProps. The resulting OriginEndpointPolicy now contains
  both the gating statement and the CdnAuthConfiguration block.
• Drops the optional cdnAuth second argument from addToResourcePolicy(...)
  on IOriginEndpoint — the field had no clean home there and only the first
  call ever applied. CDN auth now lives only on the endpoint props.
• Drops the cdnAuth prop on MediaPackageV2OriginProps for the same
  reason — set cdnAuth on the OriginEndpoint directly.
• Adds an integ test that deploys the full pipeline.
• Updates the README to document the new pattern, including the JSON shape
  the secret must use (MediaPackageV2CDNIdentifier key).

[1] https://docs.aws.amazon.com/mediapackage/latest/userguide/cdn-auth-setup.html

BREAKING CHANGE: OriginEndpoint.addToResourcePolicy() no longer accepts an
optional cdnAuth second argument. MediaPackageV2OriginProps.cdnAuth has
been removed. Set cdnAuth on OriginEndpointProps instead.

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Description of how you validated changes

Checklist

• My code adheres to the CONTRIBUTING GUIDE and DESIGN GUIDELINES

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By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

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⚠️ Experimental Feature: This security report is currently in experimental phase. Results may include false positives and the rules are being actively refined.
This security report is NOT a review blocker. Please try merge from main to avoid findings unrelated to the PR.
To suppress a specific rule, see Suppressing Rules.

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