Modify GDASApp to use crtm module

[RussTreadon-NOAA]

CRTM is cloned and built as part of the GDASApp build process. It is preferable for GDASApp to use a pre-installed CRTM module (e.g., a spack-stack CRTM module).

This issue is opened to track the changes needed to move from a GDASApp CRTM build to loading a CRTM module.

[RussTreadon-NOAA]

The following PR and issue are relevant to this issue

• JCSDA CRTMv3 PR #175
• JCSDA CRTMv3 issue 167
• JCSDA spack-stack issue #1185

[RussTreadon-NOAA]

@ADCollard and @emilyhcliu , 1 PR and 2 issues are links above regarding CRTMv3 installation and testing. Are there any more CRTMv3 issues or PRs to add to this issue for tracking purposes?

[CoryMartin-NOAA]

Biggest issue @RussTreadon-NOAA is that science validation is still happening with 2.4, so I think it may be unavoidable to go to v3 until UFO acceptance is complete. We could always have one branch that is v3 and one that is 2.4 but that might be too much overhead for maintenance.