escape terraform interpolation ${} in rulegroup

[cheskayang]

Hi grafana team,

i ran into this error when creating the RuleGroup resource
Invalid reference: A reference to a resource type must be followed by at least one attribute access, specifying the resource name.

after some digging, turns out it was caused by having ${}

example, having this in the model expression

"$ErrorsLast24h > ${PercentOfMessagesLast24h}"

should be a similar issue to #59
and

#89

currently bypassing this using $$. we use the exported rules yaml files (so once get into grafana, it will become $), would be nice to have a fix

[julienduchesne]

This should be fixed in v0.13.0!