[Custom auth ext] Highlighting policy limits to be clearer

[cilwerner]

Converting items previously added in #9314 to [!NOTE]

[learn-build-service-prod]

Learn Build status updates of commit d2ebb2c:

✅ Validation status: passed

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api-reference/beta/resources/customauthenticationextension.md	✅Succeeded

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[learn-build-service-prod]

Learn Build status updates of commit e681b50:

✅ Validation status: passed

File	Status	Preview URL	Details
api-reference/beta/api/identitycontainer-post-authenticationeventlisteners.md	✅Succeeded
api-reference/beta/resources/customauthenticationextension.md	✅Succeeded

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[learn-build-service-prod]

Learn Build status updates of commit 75510e4:

✅ Validation status: passed

File	Status	Preview URL	Details
api-reference/beta/api/identitycontainer-post-authenticationeventlisteners.md	✅Succeeded
api-reference/beta/resources/authenticationeventlistener.md	✅Succeeded
api-reference/beta/resources/customauthenticationextension.md	✅Succeeded

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[learn-build-service-prod]

Learn Build status updates of commit 0f55c5a:

✅ Validation status: passed

File	Status	Preview URL	Details
api-reference/beta/api/identitycontainer-post-authenticationeventlisteners.md	✅Succeeded
api-reference/beta/api/identitycontainer-post-customauthenticationextensions.md	✅Succeeded
api-reference/beta/resources/authenticationeventlistener.md	✅Succeeded
api-reference/beta/resources/customauthenticationextension.md	✅Succeeded

For more details, please refer to the build report.

For any questions, please:

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