Add dualnetwork test from dumux-pub repository Koch2021a

What this MR does / why does DuMux need it:

This adds the possibility to study the heat transfer between one fluid phase and a solid phase with one porenetwork model for the void space coupled to one network model for the solid phase (dualnetwork)

In addition one test case is provided with reference solutions

Notes for the reviewer

Files and test case, where taken from https://git.iws.uni-stuttgart.de/dumux-pub/Koch2021a and modified, such that it is runs on the current master

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• does the new code follow the style guide?
• do the test pipelines pass? (see guide on how to run pipelines for a merge request)
• is the code you changed and/or the new code you wrote covered in the test suite? (if not, extend the existing tests or write new ones)
• does your change affect public interfaces or behavior, or, does it introduce a new feature? If so, document the change in CHANGELOG.md.
• is the list of the header includes complete? ("include what you use")
• all files have to end with a \n character. Make sure there is no \ No newline at end of file comment in "Changes" of this MR.
• (if not applicable remove) are newly introduced or modified physical values/functions backed up with a scientific reference (including doi) in the docs?