Add targeting options to config checks (similar to subordinate rules)

[Jose Guedez]

Currently config rules have the following form:

config:
 <charm>:
  <config_item>:
   <operator>: <ref_value>

It would be helpful to have an optional condition "host-suffixes" similar to the conditions available to the subordinate checks, to target specific applications in deployments:

nrpe:
 where: container aware
 host-suffixes: [host, physical, guest]
 container-suffixes: [lxd, container]

This would help avoid false positives by narrowing checks as necessary (e.g. skip interface bonding checks in applications targeting containers)