Register risk_classification/v1 in the foundational flow catalog

What does this MR do and why?

Registers risk_classification/v1 as a foundational flow gated by duo_mr_risk_classification feature flag.

Adding the flow with a feature flag had a side-effect where RuboCop Gitlab/MarkUsedFeatureFlags cop was being triggered, so I updated the cop to consider flags inside the foundational flows configuration hash (as a best-effort attempt).

Adding the flow with a feature flag had a side-effect where RuboCop Gitlab/MarkUsedFeatureFlags cop was being triggered, so I script that collects exceptions to that cop to collect feature flags only used to gate foundational flows usage.

References

Stacked on !249559 (merged).

Part of &23131 (Phase 1)

Resolves #609305 (closed)

Resolves #609298 (closed)

Screenshots or screen recordings

Not applicable - no UI changes.

How to set up and validate locally

1. Check out this branch and run the relevant specs:

   bundle exec rspec ee/spec/models/ai/catalog/foundational_flow_spec.rb

2. Optionally, confirm the catalog item resolves in a Rails console:

   Ai::Catalog::FoundationalFlow['risk_classification/v1']

MR acceptance checklist

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