[orchagent] NVGRE Tunnel orchestration agent implementation (sonic-net#1953)

- What I did
Implemented the NVGRE Tunnel orchestration agent according to the - SONiC NVGRE Tunnel HLD

- Why I did it
Part of the NVGRE feature support.

- How I verified it
Implemented VS test.

Signed-off-by: Vadym Hlushko <[email protected]>

Author: vadymhlushko-mlnx

orchagent/Makefile.am

@@ -92,7 +92,8 @@ orchagent_SOURCES = \
             lagid.cpp \
             bfdorch.cpp \
             srv6orch.cpp \
-            response_publisher.cpp
+            response_publisher.cpp \
+            nvgreorch.cpp
 
 orchagent_SOURCES += flex_counter/flex_counter_manager.cpp flex_counter/flex_counter_stat_manager.cpp flex_counter/flow_counter_handler.cpp
 orchagent_SOURCES += debug_counter/debug_counter.cpp debug_counter/drop_counter.cpp