The hack with `either` had the side-effect that the sub-options of the
submodule didn't appear in the manual. I decided to remove this because
the "migration" isn't that hard, you just need to fix some module
declarations.
However, `mkRenamedOptionModule` wouldn't work here because it'd create
a "virtual" option for the deprecated path (i.e.
`services.grafana.provision.{datasources,dashboards}`), but that's the
already a new option, i.e. the submodule for the new stuff.
To make sure that you still get errors, I implemented a small hack using
`coercedTo` which throws an error if a list is specified (as it would be
done on 22.05) which explains what to do instead to make the migration
easier.
Also, I linkified the options in the manual now to make it easier to
navigate between those.
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