ci: Spack docker containers

[bmhan12]

This PR attempts to run Github Actions using Docker images with dependencies built with uberenv, spack.

Related to GEOS-DEV/thirdPartyLibs#261
Relates to GEOS-DEV/LvArray#318

[CusiniM]

why the need to specify both ENABLE_TRILINOS and GEOS_LA_INTERFACE?

[bmhan12]

why the need to specify both ENABLE_TRILINOS and GEOS_LA_INTERFACE?

The current way the linear algebra packages are configured in the CI jobs is by setting the ENABLE_HYPRE and ENABLE_TRILINOS variables as environment variables:

GEOS/.github/workflows/build_and_test.yml

Lines 199 to 207 in bd70903

	# The linear algebra environment variables (ENABLE_HYPRE, ENABLE_HYPRE_DEVICE & ENABLE_TRILINOS)
	# could be passed as scripts parameters as well, but a specific care must be taken to be sure
	# there's no conflict with the host-config files.
	ENABLE_HYPRE=${{ inputs.ENABLE_HYPRE }}
	ENABLE_HYPRE_DEVICE=${{ inputs.ENABLE_HYPRE_DEVICE }}
	ENABLE_TRILINOS=${{ inputs.ENABLE_TRILINOS }}
	docker_args+=(-e ENABLE_HYPRE=${ENABLE_HYPRE:-OFF})
	docker_args+=(-e ENABLE_HYPRE_DEVICE=${ENABLE_HYPRE_DEVICE:-CPU})
	docker_args+=(-e ENABLE_TRILINOS=${ENABLE_TRILINOS:-ON})

Then reading those environment variables into CMake and choosing a GEOS_LA_INTERFACE from there:

GEOS/host-configs/environment.cmake

Lines 16 to 43 in bd70903

	# If not defined as argument, take from the environment...
	if(NOT DEFINED ENABLE_HYPRE)
	set(ENABLE_HYPRE "$ENV{ENABLE_HYPRE}" CACHE BOOL "" FORCE)
	endif()
	# ... and then check the value.
	if(ENABLE_HYPRE)
	set(GEOS_LA_INTERFACE "Hypre" CACHE STRING "" FORCE)
	else()
	set(ENABLE_HYPRE OFF CACHE BOOL "" FORCE)
	endif()
	# Same pattern
	if(NOT DEFINED ENABLE_TRILINOS)
	set(ENABLE_TRILINOS "$ENV{ENABLE_TRILINOS}" CACHE BOOL "" FORCE)
	endif()
	if(ENABLE_TRILINOS)
	set(GEOS_LA_INTERFACE "Trilinos" CACHE STRING "" FORCE)
	else()
	set(ENABLE_TRILINOS FALSE CACHE BOOL "" FORCE)
	endif()
	if( (ENABLE_HYPRE AND ENABLE_TRILINOS) OR (NOT ENABLE_TRILINOS AND NOT ENABLE_HYPRE))
	MESSAGE(SEND_ERROR "Exactly one of ENABLE_HYPRE and ENABLE_TRILINOS must be defined.")
	MESSAGE(SEND_ERROR "ENABLE_HYPRE = ${ENABLE_HYPRE}.")
	MESSAGE(SEND_ERROR "ENABLE_TRILINOS = ${ENABLE_TRILINOS}.")
	endif()
	MESSAGE(STATUS "GEOS_LA_INTERFACE = ${GEOS_LA_INTERFACE}")

Instead of reading in environment variables from environment.cmake, the spack Docker containers each generate a host-config (spack-generated.cmake) to use instead, where the GEOS_LA_INTERFACE is by default set to Hypre. The snippet added here is for overriding the spack host-config defaults by defining those variables through CMake (passing them to config-build.py) instead of reading them through environment variables. This is done for CI jobs that have GEOS_LA_INTERFACE set to Trilinos.

[CusiniM]

I would remove this part about this generic command and start by saying that a spack-env file must be specified.