Feature: #12211 - Usability: Scheduler provide page browser to choose start page 

See forge#12211

Description 

To improve the usability of the linkvalidator scheduler task, the page browser is provided to choose the start page.

Impact 

Scheduler tasks that need a page uid can now add a button for the page browser popup.

In the ValidatorTaskAdditionalFieldProvider two additional fields have to be added.

'browser' => 'page',
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If the additional field browser is set to page then the SchedulerModuleController adds a button for calling the page browser popup to the field.

'pageTitle' => $pageTitle,
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The pageTitle contains the title of the page that is shown next to the browse button.