Consistently use make_shared, make_unique utilities to avoid potential memory leaks

Currently in code there is no consistent strategy for creating new objects wrapped into smart pointers. Is it recommended to use make_shared, make_unique utils to gracefully handle exceptions upon object construction: https://en.cppreference.com/w/cpp/memory/shared_ptr/make_shared
https://en.cppreference.com/w/cpp/memory/unique_ptr/make_unique

Example of code to be fixed: https://github.com/envoyproxy/envoy/blob/master/test/integration/clusters/custom_static_cluster.cc#L25