[orchagent]: Add MACsec Orchagent (sonic-net#1474)

Add MACsec orchagent for MACsec feature.
The MACsecOrch is introduced in the Orchagent to handle configuration requests. It monitors MACsec related tables in APP DB and convert those messages to SAI commands to manage the MACsec object. 
The main functions are defined in class MACsecOrch as follow
```
    task_process_status taskUpdateMACsecPort(const std::string & port_name, const TaskArgs & port_attr);
    task_process_status taskDisableMACsecPort(const std::string & port_name, const TaskArgs & port_attr);
    task_process_status taskUpdateEgressSC(const std::string & port_sci, const TaskArgs & sc_attr);
    task_process_status taskDeleteEgressSC(const std::string & port_sci, const TaskArgs & sc_attr);
    task_process_status taskUpdateIngressSC(const std::string & port_sci, const TaskArgs & sc_attr);
    task_process_status taskDeleteIngressSC(const std::string & port_sci, const TaskArgs & sc_attr);
    task_process_status taskUpdateEgressSA(const std::string & port_sci_an, const TaskArgs & sa_attr);
    task_process_status taskDeleteEgressSA(const std::string & port_sci_an, const TaskArgs & sa_attr);
    task_process_status taskUpdateIngressSA(const std::string & port_sci_an, const TaskArgs & sa_attr);
    task_process_status taskDeleteIngressSA(const std::string & port_sci_an, const TaskArgs & sa_attr);
```
 The HLD of MACsec orchagent is at [MACsec HLD](https://github.com/Azure/SONiC/blob/master/doc/macsec/MACsec_hld.md#344-macsec-orch)

Signed-off-by: Ze Gan <ganze718@gmail.com>

orchagent/Makefile.am

@@ -61,7 +61,8 @@ orchagent_SOURCES = \
             chassisorch.cpp \
             debugcounterorch.cpp \
             natorch.cpp \
-            muxorch.cpp
+            muxorch.cpp \
+            macsecorch.cpp
 
 orchagent_SOURCES += flex_counter/flex_counter_manager.cpp flex_counter/flex_counter_stat_manager.cpp
 orchagent_SOURCES += debug_counter/debug_counter.cpp debug_counter/drop_counter.cpp

orchagent/flex_counter/flex_counter_manager.cpp

@@ -7,6 +7,8 @@
 #include "logger.h"
 #include "sai_serialize.h"
 
+#include <macsecorch.h>
+
 using std::shared_ptr;
 using std::string;
 using std::unordered_map;
@@ -32,10 +34,11 @@ const unordered_map<bool, string> FlexCounterManager::status_lookup =
 
 const unordered_map<CounterType, string> FlexCounterManager::counter_id_field_lookup =
 {
-    { CounterType::PORT_DEBUG,   PORT_DEBUG_COUNTER_ID_LIST },
-    { CounterType::SWITCH_DEBUG, SWITCH_DEBUG_COUNTER_ID_LIST },
-    { CounterType::PORT,         PORT_COUNTER_ID_LIST },
-    { CounterType::QUEUE,        QUEUE_COUNTER_ID_LIST }
+    { CounterType::PORT_DEBUG,      PORT_DEBUG_COUNTER_ID_LIST },
+    { CounterType::SWITCH_DEBUG,    SWITCH_DEBUG_COUNTER_ID_LIST },
+    { CounterType::PORT,            PORT_COUNTER_ID_LIST },
+    { CounterType::QUEUE,           QUEUE_COUNTER_ID_LIST },
+    { CounterType::MACSEC_SA_ATTR,  MACSEC_SA_ATTR_ID_LIST },
 };
 
 FlexCounterManager::FlexCounterManager(

orchagent/flex_counter/flex_counter_manager.h

@@ -22,7 +22,8 @@ enum class CounterType
     PORT,
     QUEUE,
     PORT_DEBUG,
-    SWITCH_DEBUG
+    SWITCH_DEBUG,
+    MACSEC_SA_ATTR,
 };
 
 // FlexCounterManager allows users to manage a group of flex counters.