feat: Support x-xgen-atlascli in Atlas CLI example generation

[mongodb-sage-bot]

Proposed changes

The OpenAPI spec examples are generated by foascli as part of the CD
pipeline. The Atlas CLI code sample (atlas api <tag> <operationId> --help) previously honored only the x-xgen-operation-id-override
extension, but atlascli also supports the x-xgen-atlascli extension to
override the operation ID used to build the command name.

This adds support for the x-xgen-atlascli extension in the Atlas CLI
code sample generation. The operation ID is read from the nested
override.operationId field and, mirroring atlascli's command
generation, takes priority over x-xgen-operation-id-override when both
are present.

Jira ticket: CLOUDP-427938

Checklist

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

Changes to Spectral

• I have read the README file for Spectral Updates

---

Important

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This pull request was generated by sage-bot on behalf of andrea.angiolillo@mongodb.com (ticket assignee). The assignee must self-review the changes before requesting review from another engineer.
The assignee is not allowed to merge their own PR without approval from another engineer.

• andrea.angiolillo@mongodb.com has read and agrees to the MongoDB AI Policy
• andrea.angiolillo@mongodb.com has self-reviewed this PR before requesting review from another engineer

[mongodb-sage-bot]

Sage Bot can help with this pull request. Just @sage-bot in comments and I'll start working on changes in this branch.
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[mongodb-sage-bot]

Git diff is blocked by policy, but my edits are complete and verified through the Read tool. The changes are focused and consistent.

Removed the x-xgen-atlascli priority override in the Atlas CLI code sample generation in tools/foas/openapi/filter/code_sample.go; now the Atlas CLI sample (atlas api ... --help) is only emitted when an operation does not define the x-xgen-atlascli extension, since atlascli owns command generation in that case, per @andreaangiolillo's review. Also deleted the now-unused atlasCliOperationIDOverride helper and updated the corresponding test case to assert no Atlas CLI sample is produced when the extension is present.

[mongodb-sage-bot]

The changes are complete and verified via the Read tool.

Updated the x-xgen-atlascli test fixture in tools/foas/openapi/filter/code_sample_test.go to use the realistic {"skip": true} shape instead of the non-representative override.operationId form, matching how the extension actually appears in the OpenAPI spec, as @andreaangiolillo pointed out. The test still asserts no Atlas CLI code sample is emitted when the extension is present.

[mongodb-sage-bot]

My changes are complete. Both the source logic and test cases are in place.

Refined the x-xgen-atlascli handling in tools/foas/openapi/filter/code_sample.go so the Atlas CLI code sample is emitted both when the extension is missing and when it's present with "skip": false, and is only suppressed when the extension sets "skip": true. Added a skipAtlasCliCodeSample helper that checks the skip flag and a new test case for the "skip": false path (sample emitted) alongside the existing "skip": true case (sample suppressed), addressing @andreaangiolillo's feedback.

[andreaangiolillo]

LGTM