Refactor E2E tests

[whizzzkid]

Even though limited, the e2e test suite allows to run smoke tests that help identify start-up issues. All of those exist here: https://github.com/ipfs/ipfs-companion/blob/main/test/e2e/ipfs-companion.test.js

Tasks

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1. Restructure tests to leverage test lifecycle hooks before, beforeEach, after and afterEach
2. Restructure and add ergonomic methods like getFinalUrl into more reusable structures.