DOCS: Add front page cards for supported and external model implementations #1070

Job	Run time
linux-64-py	6m 10s
win-64	8m 41s
macOS	8m 16s
Standard 2-Zone Example (SANDAG)	1h 35m 7s
placeholder_multiple_zone	10m 28s
Standard 1-Zone Example (MTC)	52m 35s
prototype_marin	2m 3s
placeholder_psrc	1h 0m 39s
prototype_mtc	55m 26s
prototype_mwcog	56m 58s
production_semcog	6m 30s
prototype_mtc_extended	1h 31m 41s
prototype_sandag_xborder	5m 59s
Estimation Mode Unit Tests	24m 14s
estimation_edb_creation_test	6m 51s
Expression Profiling Tests	7m 27s
Estimation Notebooks Test	51m 53s
random_seed_generation_test	4m 16s
develop-docbuild	0s
	9h 15m 14s

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