[swss]: IcmpOrch to support ICMP session offload to ASIC

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**What I did**
IcmpOrch for supporting hardware offloaded ICMP echo sessions.
Changes done here adds support for the SAI ICMP ECHO spec:
https://github.com/opencomputeproject/SAI/blob/master/doc/SAI-Proposal-ICMP-ECHO.md

A common template in saioffloadsession.h is added for handling sai offload sessions. BFD or any future offload session handling can be migrated to this template.

IcmpOrch will create sessions based on switch capability published in STATE_DB by switchcorch which is checked in IcmpOrch's constructor.

STATE_DB SWITCH_CAPABILITY:
```
  "SWITCH_CAPABILITY|switch": {
    "value": {
<snip>
...
      "ICMP_OFFLOAD_CAPABLE": "true",
...
<snip>
    }
  },
 ```
**Why I did it**
ICMP echo sessions are used by LinkMgrd to monitor link state in Dual-ToR architecture and switch traffic.
Current software based ICMP echo sessions used by Linkprober in LinkMgrd limits the detection time and uses host network bandwidth.
Hardware based sessions will bring down the detection time and host network bandwidth is not used.

**How I verified it**
Tested the changes with DVS.

**Details if related**
ICMP echo table definitions: sonic-net/sonic-swss-common#980
ICMP echo SaiRedis changes: sonic-net/sonic-sairedis#1542

Author: mssonicbld

orchagent/Makefile.am

@@ -103,6 +103,7 @@ orchagent_SOURCES = \
             macsecorch.cpp \
             lagid.cpp \
             bfdorch.cpp \
+            icmporch.cpp \
             srv6orch.cpp \
             response_publisher.cpp \
             nvgreorch.cpp \