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/client.py

@@ -0,0 +1,40 @@
+import sys		
+import argparse
+import grpc
+
+sys.path.insert(0, '../../../../../flatbuffers/python')
+
+import flatbuffers
+from models import HelloReply, HelloRequest, greeter_grpc_fb
+
+parser = argparse.ArgumentParser()
+parser.add_argument("port", help="server port to connect to", default=3000)
+parser.add_argument("name", help="name to be sent to server", default="flatbuffers")
+
+def say_hello(stub, hello_request):
+    reply = stub.SayHello(hello_request)
+    r = HelloReply.HelloReply.GetRootAs(reply)
+    print(r.Message())
+
+def say_many_hellos(stub, hello_request):
+    greetings = stub.SayManyHellos(hello_request)
+    for greeting in greetings:
+        r = HelloReply.HelloReply.GetRootAs(greeting)
+        print(r.Message())
+
+def main():
+    args = parser.parse_args()
+
+    with grpc.insecure_channel('localhost:' + args.port) as channel:
+        builder = flatbuffers.Builder()		
+        ind = builder.CreateString(args.name)
+        HelloRequest.HelloRequestStart(builder)
+        HelloRequest.HelloRequestAddName(builder, ind)
+        root = HelloRequest.HelloRequestEnd(builder)
+        builder.Finish(root)
+        output = bytes(builder.Output())
+        stub = greeter_grpc_fb.GreeterStub(channel)
+        say_hello(stub, output)
+        say_many_hellos(stub, output)
+
+main()