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creates a pull request updating the @playwright/test package, tests fail because the Playwright Docker image is outdated.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: 99.735%. remained the same when pulling 8b064795ac1497605aa23e9c9fedf6d88cba515f on get_playwright_version_from_package_json into 5281dc0e86480789f1b3d76f55936caa458d9a01 on master.