In this commit, several changes have been made to streamline the Manufacturer and Process classes
within the ERP module:

- Replaced the non-empty check for 'firstname' and 'lastname' attributes in the User class with an
`empty()` function, resulting in cleaner code without changing the functionality.
- Replaced the argument in `User->activate()` from `false` to `''` for consistency.
- Removed unnecessary annotations and some unused `protected` properties from the Process class.
- Altered the procedure to retrieve `salesOrder` from the Entity in the Process class. Now, the
method first tries to retrieve it via `getPaymentDataEntry()`, and if unavailable, it attempts to
fetch it using `getCustomDataEntry()`. This ensures a more robust and reliable retrieval of the
'salesOrder' property.
- Added `@phpstan-ignore-next-line` in the Processes class to prevent phpstan from throwing
unwarranted warnings regarding the following code line in specific scenarios.

Related: #103

Code stability -> missing return types, qualifier imports, code cleanup, function converts to php8.1

feat: manufacturers -> setting for default manufacturer group; auto-create manufacturer group if none exists; read from product fields only if products is installed

refactor: manufacturer create -> do not pre-fetch new user id; username as required field; generate random password and auto-activate quiqqer/erp#28