Fix python header comments for some extra gRPC backends

When a Python script is to be executed directly via exec(3), either the platform knows how to execute
the file itself (i.e. special configuration is necessary) or the first line
contains a shebang (#!) specifying the interpreter to run it (similar to
shell scripts).

The shebang MUST be on the first line for the script to work on all platforms,
so any header comments need to be in the lines following it. Otherwise
executing these scripts as extra backends will yield an "exec format
error" message.

Changes:
* Move introductory comments below the shebang line
* Change header comment in transformers.py to refer to the correct
  python module

Signed-off-by: Marcus Köhler <khler.marcus@gmail.com>

backend/python/bark/ttsbark.py

@@ -1,8 +1,7 @@
+#!/usr/bin/env python3
 """
 This is the extra gRPC server of LocalAI
 """
-
-#!/usr/bin/env python3
 from concurrent import futures
 import time
 import argparse

backend/python/sentencetransformers/sentencetransformers.py

@@ -1,7 +1,7 @@
+#!/usr/bin/env python3
 """
 Extra gRPC server for HuggingFace SentenceTransformer models.
 """
-#!/usr/bin/env python3
 from concurrent import futures
 
 import argparse

backend/python/transformers/transformers.py

@@ -1,7 +1,7 @@
+#!/usr/bin/env python3
 """
-Extra gRPC server for HuggingFace SentenceTransformer models.
+Extra gRPC server for HuggingFace AutoModel models.
 """
-#!/usr/bin/env python3
 from concurrent import futures
 
 import argparse