Add Maps Control deprecation note

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

Learn Build status updates of commit 87b96a3:

:white_check_mark: Validation status: passed

File	Status	Preview URL	Details
docs/maui/get-started.md	:white_check_mark:Succeeded	View
docs/maui/views/Map.md	:white_check_mark:Succeeded	View

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