Update waf-engine.md

[yuvalpery]

Added DRS 2.1 under "support for new features"

[prmerger-automator]

@yuvalpery : Thanks for your contribution! The author(s) have been notified to review your proposed change.

[learn-build-service-prod]

Learn Build status updates of commit 46a08dc:

⚠️ Validation status: warnings

File	Status	Preview URL	Details
articles/web-application-firewall/ag/waf-engine.md	⚠️Warning		Details

articles/web-application-firewall/ag/waf-engine.md

• Line 35, Column 3: [Warning: bookmark-not-found - See documentation] Cannot find bookmark '#owasp-drs-21' in 'articles/web-application-firewall/ag/application-gateway-crs-rulegroups-rules.md', did you mean '#owasp-crs-31'?

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[Court72]

@johndowns

Can you review the proposed changes?

Important: When the changes are ready for publication, adding a #sign-off comment is the best way to signal that the PR is ready for the review team to merge.

#label:"aq-pr-triaged"
@MicrosoftDocs/public-repo-pr-review-team

[johndowns]

This should be reviewed by @vhorne (also it might make sense for you to take ownership of this article Vic?)

[johndowns]

#assign-reviewer:vhorne