Create net_peer_connection unit tests

for initial partial unit test coverage of these CConnman class methods:

- AddNode()
- ConnectNode()
- GetAddedNodeInfo()
- AlreadyConnectedToAddress()
- ThreadOpenAddedConnections()

and of the GetAddedNodeInfo() call in RPC addnode.

src/Makefile.test.include

@@ -111,6 +111,7 @@ BITCOIN_TESTS =\
   test/miniscript_tests.cpp \
   test/minisketch_tests.cpp \
   test/multisig_tests.cpp \
+  test/net_peer_connection_tests.cpp \
   test/net_peer_eviction_tests.cpp \
   test/net_tests.cpp \
   test/netbase_tests.cpp \