fix(policy): add Deny to managedDiskPublicNetworkAccess (#4204)

[Git-PrinceNagar]

Overview/Summary

The Deny-PublicPaaSEndpoints initiative's managedDiskPublicNetworkAccess parameter only exposes Audit and Disabled, while the built-in policy it maps to — 8405fdab-1faf-48aa-b702-999c9c172094 ("Managed disks should disable public network access") — also supports Deny. As a result, customers cannot enforce (deny) public network access on managed disks via this initiative.

This PR aligns the parameter with the built-in policy by adding the missing Deny value.

Fixes Azure/Azure-Landing-Zones#4204

This PR fixes/adds/changes/removes

1. Adds Deny to managedDiskPublicNetworkAccess.allowedValues (now Audit, Deny, Disabled); default remains Audit.
2. Bumps the initiative metadata.version from 5.2.0 to 5.3.0.
3. Regenerates the compiled eslzArm/managementGroupTemplates/policyDefinitions/initiatives.json via bicep build.

Breaking Changes

None. The change is additive and the default (Audit) is unchanged, so existing assignments behave exactly as before — Deny is simply now selectable.

Testing Evidence

Confirmed the built-in policy supports Deny across three independent sources:

Source	Allowed values
az policy definition show 8405fdab-... (live Azure)	Audit, Deny, Disabled
AzAdvertizer (public reference)	Audit, Deny, Disabled
Sibling param containerAppsPublicNetworkAccess (same file)	Audit, Deny, Disabled

Local validation after the fix:

• Test-BuildPolicies.Tests.ps1 (build-sync gate): 3 passed / 0 failed — committed initiatives.json matches a fresh bicep build.
• Test-ModifiedPolicies.Tests.ps1 content assertions on the modified file (version bumped, category, source, cloud environments, name/filename match, parameter default): all pass.

As part of this Pull Request I have

• Checked for duplicate Pull Requests
• Associated it with relevant issues, for tracking and closure
• Ensured my code/branch is up-to-date with the latest changes in the main branch
• Performed testing and provided evidence
• Ensured contribution guidance is followed
• Updated relevant and associated documentation
• Created a pull request to update the "What's New?" wiki page

[Git-PrinceNagar]

@microsoft-github-policy-service agree company="Microsoft"