Support configure global level client version string

[BewareMyPower]

Motivation

Currently C++ client generates a Version.h based on the Version.h.in in the templates directory when compiling. The header includes two macros:

• PULSAR_VERSION: Never used
• PULSAR_VERSION_STR: Used as the client_version field in CommandConnect

Once the library (e.g. libpulsar.so) was built, if the other libraries like the Python and Node.js wrappers use the C++ library, the client_version field could not be modified. It causes an issue that when the Python client or Node.client connectes to the broker, the version info is still the C++ client's version because these clients are based on the C++ client.

Modifications

• Add setClientVersion and getClientVersion functions to set or get the client_version field in CommandConnect.
• To not bring unnecessary mutex overhead, no mutexes are used to protect the access to the global version variable. So the setClientVersion method should be called before creating any Client object.
• Remove the template to generate Version.h.

[BewareMyPower]

Before reviewing this PR, I think we need to start a proposal since it introduces a new API. Here is the discussion before: https://lists.apache.org/thread/n59k537fhthjnzkfxtc2p4zk4l0cv3mp

I'm going to start a formal PIP soon.

[massakam]

Is it possible that users are including Version.h and using these macros? If so, removing these macros may be a breaking change.

• PULSAR_VERSION
• PULSAR_VERSION_STR

FYI, these macros were added in apache/pulsar#12769. These were originally intended to be used by the Pulsar Node.js client, but ended up not being used.
apache/pulsar-client-node#252 (comment)

[BewareMyPower]

Is it possible that users are including Version.h and using these macros?

Oh I see. It will be installed from pre-built binaries. I only checked make install does not install this header because I didn't use the project directory as the CMake directory.

And from the discussion here, we might support configuring the client version directly on a Client object. So I close this PR first.