Upgrade WebdriverIO to the latest version for all repositories

MediaWiki uses WebdriverIO, an open-source test automation framework, as it’s primary testing framework. WebdriverIO v6.0 was released just a few days back, while it's previous version, v5.0 was released in early December 2018. However, many of MediaWiki's repositories use v4.0 which has now been deprecated. WebdriverIO v6.0 brings with it a number of internal improvements that speed up test execution with lower CPU and memory usage. Upgrading to the current version would therefore be very beneficial. For this, a stepwise approach must be devised to first upgrade all repositories to v5.0 and then ultimately to v6.0.