feat: Add digest validation support to HTTP resolver

[zakisk]

This commit introduces content hash verification for the HTTP resolver by adding support for optional digest validation using SHA256 and SHA512 algorithms.

Changes:

• Add new 'digest' parameter accepting ':' format where algorithm can be 'sha256' or 'sha512'
• Implement digest validation logic using constant-time comparison to prevent timing-based side-channel attacks
• Add comprehensive unit tests covering valid matches, mismatches, invalid formats, and unsupported algorithms
• Add E2E tests to verify digest validation in real cluster scenarios
• Enable 'enable-http-resolver' feature flag in default configuration
• Update documentation with digest parameter description, usage examples, and commands to calculate SHA256/SHA512 hashes

Security considerations:

• Uses constant-time comparison to prevent timing attacks
• Digest validation is optional to maintain backward compatibility
• Digest values are logged for debugging

Fixes: #8759

Changes

Submitter Checklist

As the author of this PR, please check off the items in this checklist:

• Has Docs if any changes are user facing, including updates to minimum requirements e.g. Kubernetes version bumps
• Has Tests included if any functionality added or changed
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Release Notes

The HTTP resolver now supports optional content integrity verification through a new `digest` parameter. Users can provide a cryptographic hash in the format `<algorithm>:<hash>` (where algorithm is either `sha256` or `sha512`) to verify that the fetched content matches the expected value. For example, `digest: sha256:f37cdd0e8611932bca52eed219c2b273161501510b37218fb79ca0a6a4487cff`. This parameter is optional, ensuring backward compatibility with existing HTTP resolver configurations.

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[zakisk]

/kind feature

[zakisk]

I think that one E2E job failure is flake because before there was three jobs were failing