Use find_dependency in PackageConfig.cmake.in?

[AlexanderRichert-NOAA]

tl;dr I think we should add a find_dependency to PackageConfig.cmake.in for each corresponding find_package in CMakeLists.txt.

I don't know if we've specifically discussed whether package dependencies should automatically be propagated in CMake configs for use by downstream codes, so if we haven't then I suggest discussing here and applying a consistent approach approach NCEPLIBS.

Currently, building grib_util with the heads of develop for g2 and g2c fails because the grib_util CMake config doesn't know to look for g2c. I think that the best solution is for g2's PackageConfig.cmake.in to include find_dependency(g2c) so that the dependency is automatically propagated to CMake projects that use g2, including grib_util. This approach minimizes redundancy (avoids downstream packages needing to define those dependencies) and, maybe more importantly, it makes conditional dependency handling easy-- if package A only sometimes depends on package B depending on some build option in package A's CMakeLists.txt, then package C isn't forced to unnecessarily install and find package B if their package A installation was configured without it.