Making postgres effective_cache_size match the documentation

- https://docs.getchef.com/config_rb_chef_server_optional_settings.html
- The docs mention that the default effective_cache_size is 50% of total
  RAM, but the code hardcoded things to 128MB
Update changelog for postgres effective_cache_size change
Merge branch 'mm/effective_cache_size_master'
[OC-11712] Allow Group to Read Logfiles

* Change log_dir perms to 0750 all over
* Set perms for postgresql explictly
* Change perms to single quotes
Adjust group usage for log dirs

* Add an OmnibusHelper method to provide an owner and group hash
* Reference owner and group for log dirs in recipes where only owner is found
* Fix other recipe locations referencing node['private_chef']['user']['username'] directly