[e2e] Update references to 'networkidle' on navigation on network tests

[unlikelyzero]

Summary

The new eslint plugin for playwright advocates for navigation waits on 'domcontendloaded' over 'networkidle' for good reasons: mostly to prevent laziness and flakiness.

In our case, we have network tests which explicit need to catch the number of returned network responses/requests and the only deterministic way to do that is through 'networkidle'.

• Keep linting rule in place
• Override per network test
• Introduce @network annotation to tests which involve real network requests