- Globalize the `bootsnap.enabled` setting, under `global.rails`
- Default this to enabled for all charts
- Document it's usaged in doc/charts/globals
- Turn it off in examples/minimum configurations

We're default things to on because we found through testing that
the containers benefit even without the pre-compiled cache. We're
turning it off in minimal configurations because there is an IO spike
at container startup when the pre-compiled cache is not present.