common/telemetry: Migrate namespace into the Common namespace

Migrates the Telemetry namespace into the Common namespace to make the
code consistent with the rest of our common code.

src/core/telemetry_session.cpp

@@ -25,6 +25,8 @@
 
 namespace Core {
 
+namespace Telemetry = Common::Telemetry;
+
 static u64 GenerateTelemetryId() {
     u64 telemetry_id{};