Add ESLint check (coding guideline JS8)

I was rereading the coding guideline and wondered if "JS8: Follow guidelines set by ESLint" was checked automatically, it seems not.

Bug 23833 - [Omnibus] JavaScript should conform to coding guidelines recommended by ESLint https://bugs.koha-community.org/bugzilla3/show_bug.cgi?id=23833

Would it be worth it to have an ESLint check? (depending on the feasibility) Maybe it can be done the same way as perltidy, counting the bad lines/warnings before and after.