Speed up feature tests in CI

This MR replaces the explicit installation of spectron dependencies in the feature-tests CI job with a custom image (codingpaws/spectron-ci). The goal is to reduce repetitive and identical downloads and installations in CI and to speed up the feature-tests job.

In the container image, I was able to skip the chromedriver download and installation as spectron installs its own chromedriver anyway.

Duration delta

Before	After
job 1685949257	job 1690709098
3.0 min	1.55 min