feat: allow custom hostlist and main host #416

Job	Run time
Unit Tests	1m 53s
Formatting	25s
test-jobs (post, 100)	7m 9s
test-jobs (batch, 100)	7m 18s
test-jobs (timed, 100)	8m 3s
test-jobs (debug, 100)	7m 20s
test-jobs (volumes, 100)	7m 26s
test-jobs (hello-world, 100)	8m 24s
test-jobs (nginx-service, 100)	7m 44s
test-jobs (custom-config, 100)	7m 33s
test-jobs (minimal-service, 100)	7m 27s
test-jobs (existing-volumes, 100)	8m 23s
test-jobs (flux-resource-list, 100)	7m 40s
test-jobs (nginx-sidecar-service, 100)	8m 5s
test-jobs (pokemon, ghcr.io/rse-ops/pokemon:app-latest, 100)	8m 29s
test-jobs (snakemake, ghcr.io/rse-ops/atacseq:app-latest, 100)	9m 10s
test-jobs (singularity, ghcr.io/rse-ops/singularity:tag-mamba, 100)	7m 51s
test-jobs (lammps, ghcr.io/converged-computing/metric-lammps:latest, 100)	8m 1s
test-jobs (disable-view, ghcr.io/rse-ops/lammps:flux-sched-focal, 100)	8m 46s
	2h 17m 7s

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