slo-native output to allow creation of alert policy

[andrewmackett]

At the moment the slo-native module only outputs the Project ID. It would be really useful if the module could output the SLO name or ID. Having the SLO name or ID as an output would allow it to be used in defining the filter when creating an alerting policy for the SLO as documented here.

I've opened PR #100 to add a name output.