Add UI warning level hint to GetDigitalCredentialOption

Adds the uiWarningLevelHint property and parameter to GetDigitalCredentialOption to allow callers to indicate elevated UI warnings for sensitive requests in the credential selector UI.

Test: ./gradlew :credentials:credentials:assembleAndroidTest
Relnote: "Added `uiWarningLevelHint` to `GetDigitalCredentialOption` to support specifying warning levels in the credential selector UI."
Change-Id: Id31691a63a38c51a71a4b296a3ea78ad7debea38