Add manual examples to CI

[HLeithner]

Is your feature request related to a problem? Please describe.

We are working on step by step examples for developers. The same extensions can and should be used for automated ci tests.

Describe the solution you'd like

For each PR, download the installation files from https://github.com/joomla/manual-examples and install them.
Find a way to make this as extendable as possible, maybe only a configuration file is needed which is adding one line in the cms ci which allows to download and run specific tests from this extension.

Additional context

@muhme agreed to implement such system.

[muhme]

May 22nd created PR joomla/manual-examples#14 (waiting for merge) with first version running automated Cypress tests for all existing modul-tutorial samples