Remove sanitize-html dependency from the main bundle

What does this MR do?

The sanitize-html dependency is used by our "frequent items" dropdown for projects and groups, and this is a fairly large library. Since it pertains to something that is hidden by default, it does not make sense to require the rest of the page to wait for it to be downloaded and parsed.

This MR does two things:

• refactors frequent_items/index.js to no longer have side-effects in import
• turns frequent_items/components/app.vue into a dynamically loaded module

Screenshots

before	after

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• 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