Update ospatch's windows update classification field to be an array.

[modular-magician]

Also updates docs to display enum options in lists.
Fixes #6909.
Supports GoogleCloudPlatform/magic-modules#3820, because it allows arrays of enums to display values in docs.

Release Note Template for Downstream PRs (will be copied)

osconfig: `google_os_config_patch_deployment`'s `windows_update.classifications` field now works correctly, accepting multiple values.

all: Lists of enums now display the enum options in the documentation pages.

Derived from GoogleCloudPlatform/magic-modules#3823

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