Add ASAGI find via CMake config

[davschneller]

For the change due to TUM-I5/ASAGI#17 .

[Thomas-Ulrich]

might have been better to wait for
TUM-I5/ASAGI#17
(but I guess it is ready)

[davschneller]

Actually, this PR should make it work with "old" and "new" ASAGI. I.e. if ASAGI isn't found via CMake config, it'll resort to PkgConfig instead.
(actually, that's also a small TODO for SeisSol still)

[Thomas-Ulrich]

would it facilitate creating a pip module for easi bindings?
(then we can remove the default easi bindings to the spack package if you want ;-))

[davschneller]

Hmm; maybe—I don't know to be honest. :) Maybe I'm still out of the loop—what was the issue for that before?

[Thomas-Ulrich]

I guess it is quite involved because it depends on MPI, hdf5 and asagi.
we can also continue relying on spack, or on docker.

[davschneller]

Ok, I think I see what you mean. Then probably and sadly, the answer will still be: no, the situation hasn't really improved.
Though maybe it might be possible to just add a setup.py here—in the end, something like gmsh is also distributed via pip in binary form. (and it might be possible to split the Python package from the easi main a bit more even—by just making it a shallow adapter in some subfolder or extra repo)