Fix: enable custom donor columns in csv export

[JoshuaHungDinh]

Resolves: GIVE-923
#7398

Description

This pull request enables the filtering of the donor export csv columns. In the past, users could introduce custom columns via the give_export_donors_get_default_columns filter in the previous Donor export class. This filter was utilized in two methods:

• Displaying Custom Columns on the Tools Page: One method would display the custom columns on the donor export section of the tools page to be checked.

• Merging Custom Columns with Export Data: A second method, which incorporated custom columns into the export data.

By reintroducing this functionality in the new Donor export class, users can once again add custom donor information to the csv exports.

Affects

Donor Column Export

Visuals

Testing Instructions

• add the relevant filters to insert custom columns & data.
• export csv and verify that the custom information is printed.

Example:

    add_filter( 'give_export_donors_get_default_columns', static function($columnData) {
        $columnData['test'] = 'test-column';
        return $columnData;
    }); 


   add_filter( 'give_export_get_data_donors', static function($exportData) {
        $exportData[0]['test'] = 'test-data';
        return $exportData;
    });

Pre-review Checklist

• Acceptance criteria satisfied and marked in related issue
• Relevant @unreleased tags included in DocBlocks
• Includes unit tests
• Reviewed by the designer (if follows a design)
• Self Review of code and UX completed

[pauloiankoski]

Personally, I’m not a big fan of this approach for mainly two reasons:

1. The new method does nothing other than call a function that could be called directly.
2. Adding the hook directly to where it’s being applied helps developers easily identify it.

Regarding that, there’s nothing technically wrong, which is why I’m approving this PR.

[rickalday]

Passed manual QA tests.