[RUN AS-IF-FOSS] Replace occurrences of whitelist in Banzai module

What does this MR do?

Replace whitelist with allowlist in Banzai module.

As we are overriding some methods from html-pipeline gem, I guess to make sense to bring the upstream changes into this MR as well.

https://github.com/jch/html-pipeline/compare/v2.12.2...v2.13.2

Relates to &3478

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
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• Separation of EE specific content

Availability and Testing

• [-] Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
• [-] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• [-] Security reports checked/validated by a reviewer from the AppSec team