Enable coupling_subdomain definition by mesh tags

[arvedes]

It would be nice if it'd be possible to define the coupling_subdomain in fenicsxprecice.Adapter.initialize(coupling_subdomain, ...) by mesh tags (similar to this example). This would be especially helpful in cases with complex geometries where topological definitions are hardly possible.

I think this should be easy to implement by introducing an additional argument into the initialize function. We just have to think about how to stay consistent with the adapter for the legacy FEniCS. For a similar discussion there see precice/fenics-adapter#31.

[precice-bot]

This issue has been mentioned on preCICE Forum on Discourse. There might be relevant details there:

https://precice.discourse.group/t/fluid-solid-cht-coupling/1071/6