[example] Add 1d3d tracer example

What this MR does / why does DuMux need it:

A new documented example for a 1D-3D multi-domain problem simulating tracer transport in a porous medium with embedded transport network.

• Add fuzzy compare data regression test for the tissue tracer amount

Notes for the reviewer

Preview documentation here: https://git.iws.uni-stuttgart.de/dumux-repositories/dumux/-/blob/feature/example-1d3d/examples/embedded_network_1d3d/README.md Not all header files have been added to the documentation so far (e.g. bloodflow.hh and solver.hh are excluded). I wanted to focus on the main parts. This can be extended in the future.

Before you request a review from someone, make sure to revise the following points:

• 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)
• 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.