Add Request Blocklist case for a valid rule with missing reason

[kzar]

In the future, we might strip the "reason" field if the configuration becomes
too large, we should ensure implementations will still consider rules as valid
if we do.

---

Note

Add config example and test to validate that rules without a reason are still considered valid and block requests.

• Request Blocklist:
  • Config Reference: Add rule in request-blocklist/config-reference.json for request-blocklist.example/missing-reason with domains: ["<all>"] (no reason).
  • Tests: Add test in request-blocklist/tests.json asserting requests to /missing-reason are blocked (expectAction: "block").

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