feat(ipa): forbid custom methods on Operations endpoints

[julius-jogela]

Proposed changes

This PR adds the IPA-132 rule forbidding custom methods on Operations endpoints. The Operations resource is read-only, and control actions require mutating methods, so any :customMethod path attached to an Operations endpoint is a violation.

Jira ticket: CLOUDP-435356

Rules added

At warn severity, given $.paths with @key:

Rule	Checks
xgen-IPA-132-operations-endpoint-must-not-define-custom-methods	Any custom method path (:customMethod) whose resource identifier is an Operations endpoint — the Operations collection (.../operations) or a single Operation (.../operations/{operationId}) — is a violation

Paths with x-xgen-IPA-exception for the rule are excluded from validation. The rule name matches the guideline added in mongodb/ipa#126.

Testing

• Valid Operations endpoints, custom methods on non-Operations resources (ignored), custom methods on the Operations collection and on a single Operation in both the collection-scoped and instance-scoped forms (flagged with exact message and path), and violation-with-exception (suppressed). There is no compliant-with-exception case: every path the rule selects is a violation by definition.
• Full suite: 129 suites / 811 tests pass. gen-ipa-docs, prettier and eslint clean.
• spectral lint openapi/.raw/v2.yaml with the full ruleset: 0 xgen-IPA-132-* findings — no custom methods exist on Operations endpoints in the current spec.

Checklist

• I have signed the MongoDB CLA
• I have added tests that prove my fix is effective or that my feature works