In this commit, we have improved the handling of cron tasks and introduced the 'required'
attribute. Changes made include:

- Added 'required' attribute to three cron exec in `cron.xml` to enforce their creation.
- Updated `EventHandler` to only create `required` crons, and to stop creating non-required crons
when the `$onlyRequired` argument is set to `true`.
- Improved how crons are created with different scopes by replacing the switch statement with a
`match` expression in `EventHandler`.
- Added the handling of the 'required' attribute in `Manager` to ensure all cron objects are aware
of if they are required or not. This attribute is set to `true` for required crons and `false` if
not specified or not required.
- Simplified the array replacement in `EventHandler`.

This improvement in how cron tasks are managed will result in more efficient and robust operation
of the system.

Added a new functionality to the QUI Cron system for cleaning up cron history. These changes
include:
- An additional cron task defined in `cron.xml` for housekeeping the cron history.
- A new function called `cleanupCronHistory(array $params, Manager $CronManager)` in
`QuiqqerCrons.php` that removes old cron history entries which are older than a defined amount of
weeks.
- Added a new field and additional indexes in the `cron_history` table in `database.xml` to support
the new feature.
- New localized messages are added for the cron cleanup task 'title' and 'description' in
`locale.xml`.

Related: #59