Allow a service certificate to be specified for provisioning

[ Merge of http://go/wvgerrit/48400 ]

Client identification information has recently been enabled in
provisioning messages. For privacy concerns this information
is being encrypted with a default service certificate.
Apps need to be able to override the default one to allow
for provisioning with third party provisioning services.

Bug: 78420508
Test: WV unit, integration tests
      New WvCdmRequestLicenseTest.ProvisioningTestWithServiceCertificate test
      GTS MediaDrmTestCases

Change-Id: Iee61ad47d33ce011efbea4eb90f7e4b1f032d15f

libwvdrmengine/mediadrm/include/WVDrmPlugin.h

@@ -261,6 +261,8 @@ class WVDrmPlugin : public android::DrmPlugin,
 
   CdmIdentifier mCdmIdentifier;
 
+  std::string mProvisioningServiceCertificate;
+
   status_t queryProperty(const std::string& property,
                          std::string& stringValue) const;