Bugfix: grpc python code generation location and file suffix (#8359)

* clang-format

* [Python] Replace . with _ in grpc filename suffix

Having filenames with . like `file.fb.grcp`
is not great for Python. Since dots are used for namespaces.
Replacing all of them with _ eg suffix `foo.bar.baz` will become
`foo_bar_baz`.

Restoring the previous default `_fb` suffix.

* [Python] Use namespace in path

This fixes a regression introduced with:
fb9afbafc7
And generates the grpc file in the namespace folder again.

* Sync commandline docs with web docs

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

@@ -1,52 +1,54 @@
-# Generated by the gRPC Python protocol compiler plugin. DO NOT EDIT!
+# Generated by the gRPC FlatBuffers compiler. DO NOT EDIT!
 
+import flatbuffers
 import grpc
 
+from models.HelloReply import HelloReply
+from models.HelloRequest import HelloRequest
+
+
 class GreeterStub(object):
-  """ Interface exported by the server. """  
-  
+  '''Interface exported by the server.'''
+
   def __init__(self, channel):
-    """ Constructor. 
-    
-    Args: 
-    channel: A grpc.Channel. 
-    """
-    
+    '''Constructor.
+
+    Args:
+      channel: A grpc.Channel.
+    '''
+
     self.SayHello = channel.unary_unary(
-      "/models.Greeter/SayHello"
-      )
-    
+      method='/models.Greeter/SayHello')
+
     self.SayManyHellos = channel.unary_stream(
-      "/models.Greeter/SayManyHellos"
-      )
-    
+      method='/models.Greeter/SayManyHellos')
+
 
 class GreeterServicer(object):
-  """ Interface exported by the server. """  
-  
+  '''Interface exported by the server.'''
+
   def SayHello(self, request, context):
     context.set_code(grpc.StatusCode.UNIMPLEMENTED)
     context.set_details('Method not implemented!')
     raise NotImplementedError('Method not implemented!')
-  
-  
+
   def SayManyHellos(self, request, context):
     context.set_code(grpc.StatusCode.UNIMPLEMENTED)
     context.set_details('Method not implemented!')
     raise NotImplementedError('Method not implemented!')
-  
-  
+
 
 def add_GreeterServicer_to_server(servicer, server):
   rpc_method_handlers = {
     'SayHello': grpc.unary_unary_rpc_method_handler(
-      servicer.SayHello
-    ),
+      servicer.SayHello),
     'SayManyHellos': grpc.unary_stream_rpc_method_handler(
-      servicer.SayManyHellos
-    ),
+      servicer.SayManyHellos),
   }
+
   generic_handler = grpc.method_handlers_generic_handler(
     'models.Greeter', rpc_method_handlers)
+
   server.add_generic_rpc_handlers((generic_handler,))
 
+