[FEATURE] Clear cache of selected page in context menu

Add an entry in the context menu of the page tree to clear
the cache of the selected page.

Resolves: #20446
Releases: master
Change-Id: I1b8c7e8ed0166f7b83c9409aabf9e80245fe6799
Reviewed-on: https://review.typo3.org/48618


Tested-by: Bamboo TYPO3com <info@typo3.com>
Reviewed-by: Joerg Boesche <typo3@joergboesche.de>
Tested-by: Joerg Boesche <typo3@joergboesche.de>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>