Also search for Alberta with pkgconfig to be DUNE compliant

[blattms]

If OPM modules are used as DUNE modules then CMake otherwise complains about missing targets:

CMake Error at /usr/lib/x86_64-linux-gnu/cmake/dune-grid/dune-grid-targets.cmake:78 (set_target_properties):
  The link interface of target "dunealbertagrid1d" contains:

    PkgConfig::Alberta1d

  but the target was not found.  Possible reasons include:

    * There is a typo in the target name.
    * A find_package call is missing for an IMPORTED target.
    * An ALIAS target is missing.

upstreamed from Debian

[blattms]

Not 100% sure we really need this. I faintly recall that I/someone might have fixed this another way