PVST feature support

[bendrapubalareddy]

**** Please hold on review, will remove this line once ready for review ********** Changes: modified: cfgmgr/Makefile.am new file: cfgmgr/stpmgr.cpp new file: cfgmgr/stpmgr.h new file: cfgmgr/stpmgrd.cpp modified: configure.ac modified: orchagent/Makefile.am modified: orchagent/orchdaemon.cpp modified: orchagent/orchdaemon.h modified: orchagent/port.h modified: orchagent/portsorch.cpp modified: orchagent/saihelper.cpp new file: orchagent/stporch.cpp new file: orchagent/stporch.h new file: swssconfig/sample/00-copp.config.json modified: tests/mock_tests/Makefile.am

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