Set clusterwide attributes for more application settings

What does this MR do and why?

This solves #451957 (closed) by assigning clusterwide for all ApplicationSetting attributes.

To decide if clusterwide should be true or false I used the following reasoning (almost consistenly):

• Any setting on GitLab.com that's different from its default value should be set clusterwide: true (to keep the consistency with the current GitLab.com setup). That doesn't mean such setting couldn't be made cell-local later.
• For settings that are set as the default on GitLab.com, my assumption is that since we're using the default, we don't care if at some point certain cells start to set those with different values (after all, that's one of the benefit of Cells), so I set clusterwide: false.

The goal is to have a list of cluster-wide attributes that will be synchronized later from the leader cell to the other cells.

Note that even if a classification is wrong, it shouldn't be a big problem and the solution would only be to invert the classification. See the 2 possible scenarrii at &13165.