Extend E2E dashboard tests

[zoldar]

Changes

This PR extends previously setup E2E test suite to cover major extent of dashboard interactions.

We don't cover all the possible states, mostly focusing on "happy" paths.

The changes in the frontend code are limited to:

• adding "data-testid" attributes (and one instance of extra "data-" attribute for determining state of tab more easily)
• adding aria labels/labelledby where it makes sense

The missing coverage any cases of greater significance can be added in follow-ups as this PR is already huge. We might add more tests for less usual interaction paths but we will have to strike a balance to avoid inflating the test suite and slowing down the CI pipeline too much.

The top level tests number is kept relatively low (currently between 40-50) as state setup is usually the expensive part of the process. We might consider replacing frontend-centric fixtures setting up user and site via forms on the page with dedicated e2e endpoints in the future to reduce the time spent on it if that becomes too much of a burden (we might still keep the existing fixtures and use them only for a couple general tests to keep covering areas outside the dashboard by extension). We make extensive use of test.step to cram more test cases in each test. This means there are effectively more test cases than the report implies.

NOTE: CI is currently failing due to unrelated tests failing (they fail across other branches too). I'll have a look at them independently. Fixed!

Tests

• Automated tests definitely have been added

[apata]

Nice work! I like the sensible test data, makes the dashboard look good when running the tests in headed mode