[test] figure out a way to run e2e tests in CI

[stefanprobst]

currently, we have two issues when trying to run e2e tests in CI:

• we depend on a .auth file which must be gitignored
• we run tests against a development server (see https://github.com/acdh-oeaw/apis-oebl-research-tool-front-end/blob/development/playwright.config.ts#L76)
• we should also run tests against a backend with a test database which can be preseeded, and then reset after every test run - @sennierer would that be possible?