[TASK] Show allowed media sources in "Add media by URL" modal

In the modal view of "Add media by URL" the possible sources from where
media can be embedded are now shown.

Resolves: #82545
Releases: master, 8.7
Change-Id: I07ffedcf074b6af1e03113375f3d110916e3b034
Reviewed-on: https://review.typo3.org/54437


Reviewed-by: Jigal van Hemert <jigal.van.hemert@typo3.org>
Tested-by: Jigal van Hemert <jigal.van.hemert@typo3.org>
Reviewed-by: Sascha Rademacher <sascha.rademacher+typo3@gmail.com>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Joerg Boesche <typo3@joergboesche.de>
Tested-by: Joerg Boesche <typo3@joergboesche.de>
Reviewed-by: Henning Liebe <h.liebe@neusta.de>
Tested-by: Henning Liebe <h.liebe@neusta.de>