No option for other delimiter when exporting members

Problem/Motivation

Hard coded delimiter inside the Action Plugin Export User.

Steps to reproduce

Go inside social_user_export directory.
src/Plugin/Action/ExportUser.php

  /**
   * {@inheritdoc}
   */
  public function executeMultiple(array $entities) {
.
.
      $csv = Writer::createFromPath($file_path, 'w');
      $csv->setDelimiter(';');
      $csv->setEnclosure('"');
      $csv->setEscape('\\');
.
.

Proposed resolution

For Windows Excel Users this is an issue and for the future It might be better to give users or the admin the choice to define the delimiter.

Remaining tasks

Please expose a action setting to let users choose the delimiter.

API changes

For now I will attach a patch that changes the delimiter from "," to ";"