blog: add 2026 May monthly report

[Yilialinn]

Summary

Add the May 2026 community monthly report (EN + ZH).

Feature Highlights Covered

1. Default hmac-auth signed headers to date - PR #13388
2. Add feishu-auth plugin - PR #13382
3. Add graphql-limit-count plugin - PR #13372
4. Add error-page plugin - PR #13380
5. Add dingtalk-auth plugin - PR #13381
6. Support absolute callback URLs in cas-auth - PR #13413
7. Honor Vary header in proxy-cache memory strategy - PR #13376
8. Sign request URI cookie and tighten cookie attributes in cas-auth - PR #13331
9. Support configurable request JSON library - PR #13386
10. Add acl plugin - PR #13349
11. Add data-mask plugin - PR #13347
12. Add safer proxy-cache options - PR #13350
13. Add exit-transformer plugin - PR #13343
14. Add traffic-label plugin - PR #13342
15. Add oas-validator plugin - PR #13344
16. Support Bedrock ConverseStream streaming in ai-proxy - PR #13307
17. Support dynamic indexes in elasticsearch-logger - PR #13334
18. Rewrite Anthropic-to-OpenAI converter with whitelist body construction - PR #13321
19. Add passthrough protocol for unrecognized AI API formats - PR #13320

Contributor Statistics

• 16 contributors, 74 commits
• 6 new contributors: arpitjain099, yangkaa, hyarkoni-DN, SinhSinhAn, johannes-engler-mw, potiuk

TODO (Manual)

• Replace TODO_COVER_IMAGE_EN and TODO_COVER_IMAGE_ZH with actual cover images
• Replace TODO_CONTRIBUTOR_LIST_IMAGE with contributor list image
• Replace TODO_NEW_CONTRIBUTORS_IMAGE with new contributors image