Document "automatic" as a value for the CloseOnExit setting

[PankajBhojwani]

Closes #661

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

Learn Build status updates of commit 1eaea1b:

:white_check_mark: Validation status: passed

File	Status	Preview URL	Details
TerminalDocs/customize-settings/profile-advanced.md	:white_check_mark:Succeeded	View

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

[mattwojo]

Thanks @PankajBhojwani! Appreciate the update and issue resolution.