Python: openPMD-api release channel

Expose as module attribute.

Author: ax3l

Diff for: src/binding/python/openPMD.cpp

@@ -83,6 +83,12 @@ PYBIND11_MODULE(openPMD, m) {
         openPMDapi << "-" << OPENPMDAPI_VERSION_LABEL;
     m.attr("__version__") = openPMDapi.str();
 
+    // release channel
+    std::stringstream openPMD_release_channel;
+    if( std::string( OPENPMDAPI_RELEASE_CHANNEL ).size() > 0 )
+        openPMD_release_channel << OPENPMDAPI_RELEASE_CHANNEL;
+    m.attr("release_channel") = openPMD_release_channel.str();
+
     // feature variants
     m.attr("variants") = std::map<std::string, bool>{
         {"mpi", bool(openPMD_HAVE_MPI)},