Disable catalog refresh timer by default

Currently Onyxia refresh the catalogs every 5 minutes (see https://github.com/InseeFrLab/onyxia-api?tab=readme-ov-file#catalogs-configuration- `catalogs.refresh.ms`).
There are some caveats associated with catalog refreshs :
* In case you have multiple API pods, having one refreshed and not the other means they may be desynched resulting in user facing bugs
* Refresh may fail due to a temporary failure in registry
* Refreshing the catalogs and fetching all packages every x minutes may cause some heavy load (see #358 for possible mitigation)
* Periodic refresh on catalogs you don't maintain yourself may result in app breaking unexpectedly

I suggest we disable the refresh by default (setting `0` to `catalogs.refresh.ms` by default) while still allowing admin to override it. I also suggest we document the caveats.