Add exception message for missing rules

[Tadas]

PR Summary

Fixes #1875

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[bergmeister]

where this error is thrown, are we sure the only reason could be missing rules @Tadas ?
Kicked off CI for now to see what tests say

[andyleejordan]

@bergmeister I know we didn't get an answer to this; thoughts on merging for v1.3?

[bergmeister]

actually, on closer inspection of the diff, only 2 things are changing and they aren't of concern:

• errorMessage is passed into Exception instead of nothing, which is an improvement
• ErrorCategory is changed from ResourceExists to ResourceUnavailable, which I guess is a bit better but ObjectNotFound is maybe even better so will change it to that. This is the same category that gci notExists returns