Updating build to not fetch externals

[JessicaMeixner-NOAA]

The build currently has:
https://github.com/NOAA-EMC/WW4/blob/develop/CMakeLists.txt#L64-L79

# Google Test
include(FetchContent)
FetchContent_Declare(
    googletest
    URL https://github.com/google/googletest/archive/refs/tags/v1.14.0.zip
    DOWNLOAD_EXTRACT_TIMESTAMP TRUE
    SYSTEM
)

# yaml-cpp for configuration parsing
FetchContent_Declare(
    yaml-cpp
    URL https://github.com/jbeder/yaml-cpp/archive/refs/tags/0.8.0.zip
    DOWNLOAD_EXTRACT_TIMESTAMP TRUE
    SYSTEM
)

I do not think NCO would approve of this, but also this means we could not build WW4 from a compute node which is done in many regression testing systems for UFS and global-workflow.

I'm not sure what this is for @HendrikTolman-NOAA, but we should find an alternative path forward.

[HendrikTolman-NOAA]

@JessicaMeixner-NOAA I am addressing issues #62, #63, and #64 simultaneously in https://github.com/HendrikTolman-NOAA/WW4_HLT/tree/FT-Cmake-only-compile-system . Please take a look if this is generally what you wanted before I create a PR.

[JessicaMeixner-NOAA]

The build still fetches externals: https://github.com/HendrikTolman-NOAA/WW4_HLT/blob/FT-Cmake-only-compile-system/CMakeLists.txt#L125 even if it can be disabled, I don't think this is ideal.

Instead, I suggest adding this as submodules -- this also means you have version control of which version of these you are using.

https://git-scm.com/docs/git-submodule

[HendrikTolman-NOAA]

@JessicaMeixner-NOAA OK, I started using github submodules in the latest version. Does this look better?

[JessicaMeixner-NOAA]

Thanks! I think this will be easier to work with. The Cmake file looks much cleaner. Is this ready for me to start testing?

[HendrikTolman-NOAA]

I have not run a test with compiling this on Ursa yet, but I will effectively be out the next two weeks. If you want to test it in this branch, and suggest some tweaks, by all means do to please.