This fixes an issue with a recent addition of a config file
check in c28ded36ef.
Previously it was possible to supply a path as a string
to `configFile`. Now it will fail checking the config file
during evaluation of the module due to sandboxing.
A toggle to disable the check, more informative log messages
and handling for various configFile values are added.
- prometheus exporters are now configured with
`services.prometheus.exporters.<name>`
- the exporters are now defined by attribute sets
from which the options for each exporter are generated
- most of the exporter definitions are used unchanged,
except for some changes that should't have any impact
on the functionality.
