Add E2E tests for exploration (#6366)

* Make exploration available in e2e test env

* Add `data-testid` tags to relevant markup in exploration UI

* Write first basic test

* Add tests for featured funnel

* Extend tests

* Extract time helpers to test-utils

* Further extend the tests

* Remove the checklist

* Add missing type definition

* Fix typos

Co-authored-by: Adam Rutkowski <hq@mtod.org>

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Co-authored-by: Adam Rutkowski <hq@mtod.org>