Add v1.47.0 release of grpc-go to interop matrix (grpc#29846)

Author: dfawley

tools/interop_matrix/client_matrix.py

@@ -202,6 +202,7 @@ def __init__(self, patch=[], runtimes=[], testcases_file=None):
             ('v1.44.0', ReleaseInfo(runtimes=['go1.16'])),
             ('v1.45.0', ReleaseInfo(runtimes=['go1.16'])),
             ('v1.46.0', ReleaseInfo(runtimes=['go1.16'])),
+            ('v1.47.0', ReleaseInfo(runtimes=['go1.16'])),
         ]),
     'java':
         OrderedDict([