Test: "brownian motion" through the website

Somewhat inspired by how nicely selenium worked out for me for https://github.com/dandi/dandi-api-webshots ([its ugly dirty script is here](https://github.com/dandi/dandi-api-webshots/blob/master/tools/make_webshots.py)), I thought it would be nice if there was a test which just randomly wonders around the website (without being authenticated etc) and checks that
- no page is tuck for longer than X seconds to load
- no page returns non-ok code

I bet there should already be some helper library or tool for that -- anyone knows one?

Start by reading the linked tools/make_webshots.py script and checking this repository's existing test setup; the issue does not name an entry point or test file. Done would be an unauthenticated website test that explores pages, enforces a load-time limit, and reports any non-OK response.

Written by the indexing model from the issue text.