Change ESLint configuration

[JulianKniephoff]

Probably to @opencast/eslint-config-ts-react.

This would increase consistency between our frontend projects, and also let us get rid of a number of symptoms of us using what is basically unmaintained code:

• We currently use eslint-config-react-app, which is unmaintained.
• That holds back our ESLint version at the 8 release branch.
• It also forces the @eslint/eslintrc compatibility package on us.
• It also makes us depend on @babel/plugin-proposal-private-property-in-object because of a bug in a transitive dependency, which will never be fixed.
• It holds back our version of @typescript-eslint/typescript-estree at a version that is not compatible with the TypeScript version we use. This is probably fine (for now), but generates a fat warning during linting.
• It also generates a bunch of deprecation warnings during npm ci.

[Arnei]

I for one have no attachment whatsoever to eslint-config-react-app and am all in favor of using our own.