Add unified API landing page and fix footer layout #4331

Job	Run time
Detect File Changes	10s
Lint Gate	1m 23s
Github (ubuntu, mpi, no-debug, false)	1h 13m 53s
Github (ubuntu, mpi, no-debug, true)	1h 13m 53s
Github (macos, mpi, debug, false)	57m 56s
Github (ubuntu, mpi, debug, true)	1h 13m 51s
Github (ubuntu, no-mpi, single, no-debug, false)	28m 52s
Georgia Tech \| Phoenix (gpu-acc)	1h 14m 29s
Oak Ridge \| Frontier (AMD) (gpu-omp)	1h 13m 39s
Oak Ridge \| Frontier (gpu-omp)	1s
Oak Ridge \| Frontier (AMD) (cpu)	1s
Oak Ridge \| Frontier (gpu-acc)	1s
Github (macos, mpi, no-debug, false)	1h 14m 4s
Oak Ridge \| Frontier (cpu)	1s
Georgia Tech \| Phoenix (cpu)	1h 14m 29s
Georgia Tech \| Phoenix (gpu-omp)	1h 14m 32s
Github (ubuntu, mpi, debug, false)	1h 13m 50s
	12h 35m 5s

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