[sonic-utilities] Add Python 3 sonic-yang-mgmt package as a dependency (

sonic-net#5903)

Add Python 3 sonic-yang-mgmt package as a dependency in sonic-utilities makefile.

Recently updated the sonic-utilities Jenkins build environment [here](Azure/sonic-build-tools#185) to begin running tests on the Python 3 version of the sonic-utilities package. However, the build is failing because it attempts to copy the Python 3 sonic-yang-mgmt package from the artifacts of the latest VS build, but the package does not exist because there are no targets which specify it as a dependency. This PR will ensure the Python 3 package is built during the image build process.

rules/sonic-utilities.mk

@@ -15,6 +15,7 @@ $(SONIC_UTILITIES_PY2)_DEPENDS += $(SONIC_PY_COMMON_PY2) \
                                   $(SWSSSDK_PY2) \
                                   $(SONIC_CONFIG_ENGINE_PY2) \
                                   $(SONIC_YANG_MGMT_PY2) \
+                                  $(SONIC_YANG_MGMT_PY3) \
                                   $(SONIC_YANG_MODELS_PY3)
 $(SONIC_UTILITIES_PY2)_DEBS_DEPENDS = $(LIBYANG) \
                                       $(LIBYANG_CPP) \