Incorporate mutation testing in order to improve code quality

[MateuszNaKodach]

Goal
Test your tests with mutation testing.

Subtasks

• Configure Stryker mutator
• Add in package.json script to run mutation testing
• Run mutation testing for PullRequest only if there are changes for api package.
• Add mutation testing badge for api package

Helpful resources

• https://stryker-mutator.io/
• Example project with Stryker: https://github.com/nowakprojects/CodersCamp2020.Project.FullStack-Node-React.TableSoccerTournaments/tree/develop/backend

[MateuszNaKodach]

@KrystianKjjk the same tool is very useful in .NET.
I'd be good for you to get familiar with that.