Testing environment - upgrade Karma to the latest version

[pomek]

📝 Provide a description of the new task

As in the title, due to:

(node:60317) [log4js-node-DEP0004] DeprecationWarning: Pattern %d{DATE} is deprecated due to the confusion it causes when used. Please use %d{DATETIME} instead.

Unfortunately, Karma@6 introduced a few breaking changes that touch our env.

[pomek]

After upgrading to Karma 6, the following warning is reported:

16 03 2022 12:15:34.369:WARN [karma-server]: Passing raw CLI options to `new Server(config, done)` is deprecated. Use `parseConfig(configFilePath, cliOptions, {promiseConfig: true, throwErrors: true})` to prepare a processed `Config` instance and pass that as the `config` argument instead.

[pomek]

Scope

• Upgrade karma from 5 to 6
• When executing tests, it prints the deprecated warning.
• Rewrite a part of the code to drop the "deprecated warning".
• Make sure all supported options still work (see the testing env. guide).
• The intellijkarmarunner plugin must work.
• Perhaps it's a good occasion to refactor the runautomatedtests.js file (e.g. a function should not be defined as a string).

[pomek]

TODO: Report a follow-up issue for upgrading karma in the following repositories:

• Package generator
• Inspector
• Integrations (2x Vue, React, perhaps Angular too).

[psmyrek]

Issues for upgrading Karma have been created:

• Package generator https://github.com/ckeditor/ckeditor5-package-generator/issues/92
• Integrations https://github.com/ckeditor/ckeditor5-vue/issues/210 https://github.com/ckeditor/ckeditor5-vue2/issues/18 https://github.com/ckeditor/ckeditor5-angular/issues/308 https://github.com/ckeditor/ckeditor5-react/issues/292
• Inspector (no issue, Karma is already up-to-date 🎉)