[Admin] (preprocessor) Handle Local option

[ElizabethSamuel-MSFT]

Also taking the opportunity to clean up the CDN option

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

Learn Build status updates of commit 413fd45:

:white_check_mark: Validation status: passed

File	Status	Preview URL	Details
generate-docs/scripts/preprocessor.ts	:white_check_mark:Succeeded

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