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
- [ ] Restructure tests to leverage test lifecycle hooks `before`, `beforeEach`, `after` and `afterEach`
- [ ] Restructure and add ergonomic methods like `getFinalUrl` into more reusable structures.