Don't sync group settings by default

Google's groups-settings API has rate-limiting and other reliability issues that make it very difficult and slow to read the existing settings of all groups, so update the sync tool to not sync the group settings for existing groups by default.

There should still be a option to sync the settings, in case we need to change them.

In theory, since Google's groups-settings API has rate limiting of 1000 queries per 100s and we have around 6600 groups, it should be sufficient to set http_retry_delay to 100 and http_retries to 6 to ensure that the settings of all groups can be read. In practice, around 25-30 retries are needed.