Add disable_gravatar and federated_avatar

.env.sample

@@ -11,6 +11,8 @@ GITEA_DISABLE_REGISTRATION=false
 GITEA_ENABLE_NOTIFY_MAIL=true
 GITEA_ENABLE_OPENID_SIGNIN=true
 GITEA_ENABLE_OPENID_SIGNUP=true
+GITEA_DISABLE_GRAVATAR=false
+GITEA_ENABLE_FEDERATED_AVATAR=true
 
 GITEA_MAILER_FROM=noreply@example.com
 GITEA_MAILER_USER=noreply@example.com