Pass through BUILD_REPOSITORY_NAME to docker containers (#8407)

Needed for manifest generation. Previously we used the uri for the name
of the build, but the name is also used for generating the names of the
stable package feeds.

Co-authored-by: dotnet-bot <dotnet-bot@dotnetfoundation.org>

eng/dockerrun.sh

@@ -160,6 +160,7 @@ docker run $INTERACTIVE -t --rm --sig-proxy=true \
     -e _PACKAGEVERSIONPROPSURL \
     -e EXTERNALRESTORESOURCES \
     -e BUILD_REPOSITORY_URI \
+    -e BUILD_REPOSITORY_NAME \
     -e BUILD_SOURCEBRANCH \
     -e BUILD_BUILDNUMBER \
     -e BUILD_BUILDID \