feat: add service account API key management endpoints (#161)

## Summary

- Added three new **Service Accounts** API endpoints to the OpenAPI
spec: list API keys (GET), create API key (POST), and revoke API key
(DELETE)
- Added a "Service Accounts" navigation group to the API Reference
section
- Updated the `list_attestations_for_criteria` endpoint to document the
400 error response when `commit_list` is missing, and the 422 response
for invalid attestation types
- Updated the attestation endpoint description to clarify that
`commit_list` is required

Co-authored-by: mintlify[bot] <109931778+mintlify[bot]@users.noreply.github.com>

Author: mintlify[bot]