Upgrade CMake minimum required version to 3.16

[dbarker]

In order to upgrade several of the project's dependencies (googletest, benchmark, grpc, protobuf) to more recent versions (See #3525) we'll need to upgrade the CMake minimum required version to 3.16. This issue is to track that effort.

Seeking feedback! Please post in the thread below with any feedback/concerns about the CMake min version bump to 3.16.

[marcalff]

CMake 3.16 sounds good.

[lalitb]

+1