doc: update flux_reactor_create(3) flags #2523

Job	Run time
Generate build matrix	8s
python linting	28s
spelling	8s
validate commits	0s
bookworm - test-install	12m 23s
bookworm - 32 bit	13m 1s
noble - test-install	12m 41s
el9 - test-install	12m 16s
alpine - test-install	12m 22s
fedora40 - test-install	11m 57s
jammy - test-install	12m 21s
focal - py3.8	16m 52s
bookworm - gcc-12,content-s3,distcheck	19m 52s
fedora40 - clang-18	16m 30s
coverage	24m 48s
el8 - ascii	19m 35s
el8 - test-install	13m 10s
el8 - system,coverage	7m 54s
inception	21m 56s
flux-accounting check	4m 33s
flux-pam check	4m 7s
flux-pmix check	13m 19s
macos build only	3m 14s
flux-sched check	6m 53s
Generate docker manifest	1s
	4h 20m 29s

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