Resolve flaky e2e test

[tijmenbruggeman]

Fixes the test "will only apply a conversion when images are already compressed but not converted". This test verifies that bulk optimization still converts images even if they have already been compressed.

Test script of this test

- turns off conversion
- uploads & compresses an image
- turns on conversion
- uploads an image
- uses bulk optimization to convert the first image and convert & compress the second one

The test was flaky because the network request happening in the bulk optimization script wasn't awaited and the table row therefor could not always be found in the right state.

• modernized JavaScript to make it more readable;
• added a test id to the table rows;
• added an endpoint await;
• added an set api key to ensure the test can be run individually;