ESLint fixes and unified lint targets (#3424)

* optimise lint targets

* fix eslint config files

* fix app coverage settings

* tune eslint to warn about optional chains

app/karma.conf.js

@@ -1,11 +1,15 @@
 // Karma configuration file, see link for more information
 // https://karma-runner.github.io/1.0/config/configuration-file.html
+const { join } = require('path');
 const getBaseKarmaConfig = require('../karma.conf');
 
 module.exports = function (config) {
   const baseConfig = getBaseKarmaConfig();
   config.set({
     ...baseConfig,
-    coverageReporter: {},
+    coverageReporter: {
+      ...baseConfig.coverageReporter,
+      dir: join(__dirname, '../coverage/content-ce')
+    }
   });
 };