docs: add tests page

[qhantom]

DESCRIPTION

This PR adds a "Testing" page to the docs.

TO-DO

• [x] implement and update tests
• [x] update docs
• [x] pull main & resolve merge conflicts
• [x] check Vercel deployment

CLOSES

Closes #517

[vercel[bot]]

The latest updates on your projects. Learn more about Vercel for Git ↗︎

Name	Status	Preview	Updated (UTC)
app	✅ Ready (Inspect)	Visit Preview	Apr 11, 2024 7:08am
docs	✅ Ready (Inspect)	Visit Preview	Apr 11, 2024 7:08am

[nx-cloud[bot]]

☁️ Nx Cloud Report

CI is running/has finished running commands for commit b74ada03e309bc1400eb164f9413b017aa3c2667. As they complete they will appear below. Click to see the status, the terminal output, and the build insights.

📂 See all runs for this CI Pipeline Execution

---

✅ Successfully ran 2 targets

- [`nx build @frachtwerk/essencium-app`](https://cloud.nx.app/runs/duWQYZjBoJ?utm_source=pull-request&utm_medium=comment) - [`nx affected --target=lint --parallel=10`](https://cloud.nx.app/runs/JI5oU4UAvo?utm_source=pull-request&utm_medium=comment)

---

Sent with 💌 from NxCloud.