feat(cloud): add cost report endpoints (Beta)

[joshrotenberg]

Summary

Add support for the Cost Report API endpoints (currently in Beta).

Endpoints to implement

Library (redis-cloud)

• POST /cost-report - Generate cost report
• GET /cost-report/{costreportId} - Get cost report

CLI (redisctl)

• cloud account generate-cost-report - Generate a cost report
• cloud account get-cost-report <id> - Get cost report by ID

Notes

• These endpoints are marked as Beta in the API documentation
• May require async operation handling (POST returns task ID)

References

• Redis Cloud API Docs

[joshrotenberg]

Implemented in PR #479