Converts .eslintrc.yml to the new flat file eslint configuration format

[kemelzaidan]

Eslint has recently converted from the legacy .eslintrc.yml file to a new flat file configuration: https://eslint.org/docs/latest/use/configure/migration-guide.

So, the lint wasn't working anymore. I have migrated the file to the new format and also took the step to change the max-len from 80 (which wasn't being enforced since it used to generate so many errors) to a more flexible 120 characters, which usually adapts well in any modern screen and is also generating only 6 errors.