Add ZMQ port for orchagent (sonic-net#795)

Add ZMQ port for orchagent.

#### Work item tracking
Microsoft ADO (number only): 17753804

#### Why I did it
Orchagent need create ZMQ server for listen incoming connection.

#### How I did it
Add ZMQ address to zmqserver.h

#### How to verify it
Pass all UT and E2E test cases.

#### Which release branch to backport (provide reason below if selected)

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- Note we only backport fixes to a release branch, *not* features!
- Please also provide a reason for the backporting below.
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- [x] 202006
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- [ ] 201811
- [ ] 201911
- [ ] 202006
- [ ] 202012
- [ ] 202106
- [ ] 202111

#### Description for the changelog
Add ZMQ port for orchagent.

#### Link to config_db schema for YANG module changes
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Provide a link to config_db schema for the table for which YANG model
is defined
Link should point to correct section on https://github.com/Azure/SONiC/wiki/Configuration.
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#### A picture of a cute animal (not mandatory but encouraged)

common/zmqserver.h

@@ -11,6 +11,9 @@
 #define MQ_POLL_TIMEOUT (1000)
 #define MQ_WATERMARK 10000
 
+/***** ZMQ PORT *****/
+static const int ORCH_ZMQ_PORT = 8020;
+
 namespace swss {
 
 class ZmqMessageHandler