Make handling of federation Authorization header (more) compliant with RFC7230 (#12774)

The main differences are:
- values with delimiters (such as colons) should be quoted, so always
  quote the origin, since it could contain a colon followed by a port
  number
- should allow more than one space after "X-Matrix"
- quoted values with backslash-escaped characters should be unescaped
- names should be case insensitive

synapse/http/matrixfederationclient.py

@@ -747,7 +747,7 @@ class MatrixFederationHttpClient:
         for key, sig in request["signatures"][self.server_name].items():
             auth_headers.append(
                 (
-                    'X-Matrix origin=%s,key="%s",sig="%s",destination="%s"'
+                    'X-Matrix origin="%s",key="%s",sig="%s",destination="%s"'
                     % (
                         self.server_name,
                         key,