feat: add attributes to createCustomer function

See merge request !56

This commit includes enhancements in customer creation feature. Specifically, it modifies the
`createCustomer` function by adding a new parameter `$attributes` to handle attribute data during
customer creation process. Moreover, it introduces UI components to collect these attribute
details. Updates have been made to the associated form elements, button actions and display methods
to accommodate these changes. In addition, it makes considerable changes in the backend JavaScript
files to facilitate frontend changes and to meet compatibility.

There's also a change in error handling part where it replaces the `try-catch` block, which attempt
to get the standard address, with direct command. This assures the retrieval of the standard
address, if exists, else a new address will be created implicitly.

Finally, few general code improvements are done like changing usage of `var` to `const` or `let`
where necessary for better maintainability. A minor adjustment on window height property is also
made in `CustomerWindow.js` file.

Related: #68

fix: show tel fax input at customer creation window

See merge request !55

fix: missing customer number for new users

See merge request !53

Automatic customer number assignment when ordering

Add QUIQQER Tooling

See merge request !36

fix: open items list has UUID of the user in the file name

See merge request !52

related: pcsg/buero#443

Next 2.x

Closes pcsg/buero#439

See merge request !51

fix: customer select control - 0 user

See merge request !49

related: pcsg/buero#415

related: pcsg/buero#415

fix: customer selection control Double-click behaviour

See merge request !48

related: pcsg/buero#415

related: pcsg/buero#415

The behaviour of the customer window has been completely revised.
An attempt has been made not to produce such constant flickering.

related: pcsg/buero#415

fix: post incoming payments

See merge request !47

related: pcsg/buero#421

fix: file attachments cannot be downloaded via hash

See merge request !46

related: pcsg/buero#419

fix: customer user extra fields migration

See merge request !45