Add no-unused-vars rule

[fvoska]

I propose we add no-unused-vars rule to @infinumjs/eslint-config-core-js.

In TS projects, we sometimes set these two compiler flags:

"noUnusedLocals": true,
"noUnusedParameters": true,

but that made debugging tedious.

If we add eslint rule for unused variables, we can disable those TS flags so that recompile works when debugging. Still, the codebase should not contain any unused variables because it should now be covered by eslint