Add rule_id field to Policy to identify matched rule

[annacai21]

Adds a rule_id field to the Policy table in the FlatBuffers schema so an evaluation outcome can be traced back to the rule that produced it. For Remote Config rules this carries the rule's UUID; for hardcoded/built-in policies it is the label "hardcoded".

This is the schema groundwork for surfacing the deciding rule in injection telemetry and linking a skipped or instrumented process back to its rule on the Instrumentation Rules page.

[datadog-official]

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

🎯 Code Coverage (details)
• Patch Coverage: 100.00%
• Overall Coverage: 21.66%

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[iamluc]

I thought the rule_id would be added to a node, not to Policy 🤔

Also the comment looks wrong. It says UUID or "hardcoded" sentinel, but I believe the RFC says it could be an UUID, or a description, or the "hardcoded" sentinel

[annacai21]

I updated the RFC to say that we're putting rule_id on Policy. For RC policies, one rule compiles to one Policy, so it makes more sense to add this field here instead of to a node that's just one condition of a rule. It's also simpler on the engine side: the action fires for the matched Policy, so the engine can read Policy.rule_id directly, without having to pick out which node within the rule carries the id.

I also updated the doc so rule_id only ever contains the UUID the backend already uses (here) or the string "hardcoded". It does not contain the description.