[INFRA] Include e2e tests in the code coverage measure

[tbouffard]

Coverage measured value of bpmn-visualization@0.8.0 in sonarcloud is 55.3%.
It doesn't count the code that is only tested through HTML page: this is mainly mxGraph extension code that we have decided to only tested in the Browser because we are interested in the final rendering more than what is in the DOM.

This is now more visible as we have made coverage percentage visible through SonarCloud.

See puppeteer coverage: https://pptr.dev/#?product=Puppeteer&version=v5.4.1&show=api-class-coverage

[tbouffard]

Temporar solution: to avoid the PR to be marked as failed, I have created a dedicated Sonar Quality Gate (based on the Sonar way Gate we previously used) that is now used by the project

[tbouffard]

First attempt done with #1024: we are waiting for support of sourcemap to make the coverage use the Typescript code instead of the development bundle js code.