Issue #3317188 by idebr: Implement a primary button in Action configuration form

    // :D Make sure the submit button is at the bottom of the form

    // and is editable from the action buildConfigurationForm method.

    $form['actions'] = [

      '#type' => 'actions',

      '#weight' => 666,

    ];

    $form['actions'] = ['#type' => 'actions'];

    $form['actions']['submit'] = [

      '#type' => 'submit',

      '#button_type' => 'primary',

      '#value' => $this->t('Apply'),

      '#submit' => [

        [$this, 'submitForm'],

      ],

    ];

    $this->addCancelButton($form);