Get the Playwright version from the package.json

[elchininet]

To run the end-to-end tests we execute Playwright using a spcific Docker tag. To know the docker tag that we need to use, we read the Playwright Docker image tag from a file placed in the root of the project. This provokes that everytime @dependabot creates a pull request updating the @playwright/test package, tests fail because the Playwright Docker image is outdated.

In this pull request, we read the Playwright version from the same package.json and in this way, we can remove the necessity of having the .playwright_docker_version at all.

[coveralls]

coverage: 100.0%. remained the same
when pulling c8f308e on get_playwright_version_from_package_json
into a24b5e9 on master.