Working on a python example plus fixing python grpc code (#6456)

Refactored python grpc code gen

Adds example server & client + fixes ci

Fixes generated code

Making sure we encode the reply string as utf8

Adds Readme details to clarify issue regarding encoding when python is sending/receiving

grpc/examples/python/greeter/models/HelloReply.py

@@ -0,0 +1,45 @@
+# automatically generated by the FlatBuffers compiler, do not modify
+
+# namespace: models
+
+import flatbuffers
+from flatbuffers.compat import import_numpy
+np = import_numpy()
+
+class HelloReply(object):
+    __slots__ = ['_tab']
+
+    @classmethod
+    def GetRootAs(cls, buf, offset=0):
+        n = flatbuffers.encode.Get(flatbuffers.packer.uoffset, buf, offset)
+        x = HelloReply()
+        x.Init(buf, n + offset)
+        return x
+
+    @classmethod
+    def GetRootAsHelloReply(cls, buf, offset=0):
+        """This method is deprecated. Please switch to GetRootAs."""
+        return cls.GetRootAs(buf, offset)
+    # HelloReply
+    def Init(self, buf, pos):
+        self._tab = flatbuffers.table.Table(buf, pos)
+
+    # HelloReply
+    def Message(self):
+        o = flatbuffers.number_types.UOffsetTFlags.py_type(self._tab.Offset(4))
+        if o != 0:
+            return self._tab.String(o + self._tab.Pos)
+        return None
+
+def Start(builder): builder.StartObject(1)
+def HelloReplyStart(builder):
+    """This method is deprecated. Please switch to Start."""
+    return Start(builder)
+def AddMessage(builder, message): builder.PrependUOffsetTRelativeSlot(0, flatbuffers.number_types.UOffsetTFlags.py_type(message), 0)
+def HelloReplyAddMessage(builder, message):
+    """This method is deprecated. Please switch to AddMessage."""
+    return AddMessage(builder, message)
+def End(builder): return builder.EndObject()
+def HelloReplyEnd(builder):
+    """This method is deprecated. Please switch to End."""
+    return End(builder)