Update Knot Resolver to version 5.4.0

Recently, there was released a new version 5.4.0 of Knot Resolver. Changelog: https://www.knot-resolver.cz/2021-07-29-knot-resolver-5.4.0.html

Would it be possible to take a look? This should be send to develop branch of this repository, so we can include it in minor release.

Knot Resolver runs on Turris Omnia and Turris MOX (Shield). Once you do run time testing, then it needs to be send to the upstream repository. In this case, I'm talking about packages feed.