az sig gallery-application doesn't accept sas uris when creating from az cli

**az sig gallery-application version create** fails with the following error when I try to provide a SAS URI. However, the same works when using Azure portal to create a new version (easy to verify when you create from the portal and use the browse option for "Source application package")

- ERROR: (InvalidParameter) Source uri: '"https://.blob.core.windows.net//?sp=r&sv=2021-06-08&sr=b&sig=***************************************"' must be an absolute uri.
- Code: InvalidParameter
- Message: Source uri: '"https://.blob.core.windows.net//?sp=r&sv=2021-06-08&sr=b&sig=***************************************" must be an absolute uri.
- Target: galleryApplicationVersion.properties.publishingProfile.source.mediaLink

Start by reproducing the az sig gallery-application version create request with the SAS URI shown in the issue, then compare it with the Azure portal's source application package request. Trace the gallery application version API specification and its source.mediaLink validation; done means a valid SAS URI is accepted without the reported absolute-URI error.

Written by the indexing model from the issue text.