Update app-onboarding.md

[canibal]

changing links to policy creation documentation

[learn-build-service-prod]

Learn Build status updates of commit 8d16916:

⚠️ Validation status: warnings

File	Status	Preview URL	Details
CloudAppSecurityDocs/app-onboarding.md	⚠️Warning		Details

CloudAppSecurityDocs/app-onboarding.md

• Line 29, Column 3: [Warning: hard-coded-locale - See documentation] Link 'https://learn.microsoft.com/en-us/defender-cloud-apps/access-policy-aad' contains locale code 'en-us'. For localizability, remove 'en-us' from links to most Microsoft sites.
• Line 30, Column 3: [Warning: hard-coded-locale - See documentation] Link 'https://learn.microsoft.com/en-us/defender-cloud-apps/session-policy-aad' contains locale code 'en-us'. For localizability, remove 'en-us' from links to most Microsoft sites.
• Line 29, Column 3: [Suggestion: docs-link-absolute - See documentation] Absolute link 'https://learn.microsoft.com/en-us/defender-cloud-apps/access-policy-aad' will be broken in isolated environments. Replace with a relative link.
• Line 30, Column 3: [Suggestion: docs-link-absolute - See documentation] Absolute link 'https://learn.microsoft.com/en-us/defender-cloud-apps/session-policy-aad' will be broken in isolated environments. Replace with a relative link.

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