Steps to reproduce

1.  Create and run an ABn test for travel/about.html.
2.  Repeatedly request that page via curl (curl -v http://localhost:8080/magnoliaPublic/travel/about.html)

Expected results

Every request is handled by ABTestingFilter#doFilter

Actual results

Only the first request is handled by ABTestingFilter#doFilter

Workaround

Add a config.modules.cache.config.contentCaching.defaultPageCache.cachePolicy.shouldBypassVoters.urls.excludes.travel.yaml excluding the page URL from caching

Development notes

• This PR adds logging ABTestingFilter#doFilter, which simplifies observing expected and actual results.
• One approach to solving this could be to exclude requests from the cache that have the X-Header (from ABTEST-430) set. For this we would need to add a cache policy based on info.magnolia.voting.voters.RequestParameterVoter
• An alternative approach is to disable caching of pages under test via a TTL voter similar to how this is done in the personalisation module with info.magnolia.personalization.cache.PersonalizedContentTtlVoter.