[DOCS] Fix warnings of rendering ext:dashboard

* Fix broken indentation
* Add missing blank line
* Fix wrong used reference target
* Add missing interface to docs, which already was referenced

Resolves: #91199
Releases: master
Change-Id: If42021e0f7b4a0b879ba5be6bde9112b6c7e658d
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/64322


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Björn Jacob <bjoern.jacob@tritum.de>
Tested-by: Richard Haeser <richard@maxserv.com>
Reviewed-by: Björn Jacob <bjoern.jacob@tritum.de>
Reviewed-by: Richard Haeser <richard@maxserv.com>