feat(rulesets): improve handling of id and ref unknown values

[jacobbednarz]

Updates the schema definition to apply
stringplanmodifier.UseStateForUnknown on the values as once they are set, they should not be changing and we can safely rely on the values.

This is the last piece of the rulesets drift issue.

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[zakcutner]

We actually shouldn't mark either of the id or ref fields as UseStateForUnknown. This is because they will change across updates to the ruleset, so adding this will cause the provider to emit an incorrect plan. This is because the API cannot know which rules in the new version of the ruleset map to which rules in the previous version (i.e., rules might have been reordered, rules might have been added or deleted, etc.).

The way around this is to give each rule an explicit ref (by default, the ref is set to the same as the id). This way, the API knows which rule ids to keep the same in the new version, by looking at which refs have remained the same. The custom plan modifier that was added in #4697 will show the correct diff in this case, by matching rule refs in the state and the plan against each other.