Add configs to make profile data more private (#9203)

Add off-by-default configuration settings to:
- disable putting an invitee's profile info in invite events
- disable profile lookup via federation

Signed-off-by: Andrew Ferrazzutti <fair@miscworks.net>

synapse/config/federation.py

@@ -41,6 +41,10 @@ class FederationConfig(Config):
         )
         self.federation_metrics_domains = set(federation_metrics_domains)
 
+        self.allow_profile_lookup_over_federation = config.get(
+            "allow_profile_lookup_over_federation", True
+        )
+
     def generate_config_section(self, config_dir_path, server_name, **kwargs):
         return """\
         ## Federation ##
@@ -66,6 +70,12 @@ class FederationConfig(Config):
         #federation_metrics_domains:
         #  - matrix.org
         #  - example.com
+
+        # Uncomment to disable profile lookup over federation. By default, the
+        # Federation API allows other homeservers to obtain profile data of any user
+        # on this homeserver. Defaults to 'true'.
+        #
+        #allow_profile_lookup_over_federation: false
         """