Set up project substitution for client:transport

This ensures that projects depending on client:transport (such as client:benchmark) properly resolve this dependency.

build.gradle

@@ -166,6 +166,7 @@ subprojects {
     "org.elasticsearch.client:rest:${version}": ':client:rest',
     "org.elasticsearch.client:sniffer:${version}": ':client:sniffer',
     "org.elasticsearch.client:test:${version}": ':client:test',
+    "org.elasticsearch.client:transport:${version}": ':client:transport',
     "org.elasticsearch.test:framework:${version}": ':test:framework',
     "org.elasticsearch.distribution.integ-test-zip:elasticsearch:${version}": ':distribution:integ-test-zip',
     "org.elasticsearch.distribution.zip:elasticsearch:${version}": ':distribution:zip',