Enhance clarity for workaround with unsupported Connection String Types

[neoscie]

This commit expands the workaround for connection string types that are not properly handled by the EnvironmentVariablesConfigurationProvider, as detailed in the already referenced issue. It clarifies that the "Custom" connection string type should be used not only for PostgreSQL but also for Notification Hub, Service Bus, Event Hub, Document Db and Redis Cache.

Additionally, this update completes the list of connection string types currently available in Azure App Service, along with their respective environment variable prefixes, ensuring comprehensive guidance for users.

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Learn Build status updates of commit d7940fc:

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[Jak-MS]

@cephalin

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[learn-build-service-prod[bot]]

Learn Build status updates of commit 3f82e7c:

:white_check_mark: Validation status: passed

File	Status	Preview URL	Details
articles/app-service/configure-common.md	:white_check_mark:Succeeded

For more details, please refer to the build report.

For any questions, please:

• Try searching the learn.microsoft.com contributor guides
• Post your question in the Learn support channel