Add setup check for background blur + documentation #6503
Description
- There should be a setup check in
settings/admin/overvieworsettings/admin/talk - There should be a comment in our docs: https://nextcloud-talk.readthedocs.io/en/latest/system-requirements/#webserver
- The default setup in Nextcloud docs should be adjusted like in https://github.com/nextcloud/documentation/pull/930/files