[5.2][Events] Use event classes for Sampledata plugins

[Fedik]

Summary of Changes

Update sampledata plugins to use SubscriberInterface and event classes.

Testing Instructions

Try to install sample data, of each type. All should work as before.

Actual result BEFORE applying this Pull Request

Works

Expected result AFTER applying this Pull Request

Works

Link to documentations

Please select:

• [ ] Documentation link for docs.joomla.org:
• [ ] No documentation changes for docs.joomla.org needed
• [x] Pull Request link for manual.joomla.org: https://github.com/joomla/Manual/pull/177
• [ ] No documentation changes for manual.joomla.org needed