WIP: allow mustache templates in job environment variables #10014

Job	Run time
validate commits	13s
spelling	8s
Generate build matrix	10s
python linting	27s
bookworm - test-install	12m 0s
bookworm - 32 bit	12m 45s
noble - test-install	12m 35s
el9 - test-install	12m 19s
alpine - test-install	13m 12s
fedora40 - test-install	11m 39s
jammy - test-install	11m 58s
focal - py3.8	16m 34s
bookworm - gcc-12,content-s3,distcheck	19m 53s
fedora40 - clang-18	16m 36s
coverage	24m 4s
el8 - ascii	19m 14s
el8 - test-install	13m 19s
el8 - system,coverage	7m 41s
inception	21m 15s
flux-pam check	4m 19s
flux-pmix check	13m 13s
macos build only	3m 18s
flux-accounting check	4m 45s
flux-sched check	6m 55s
Generate docker manifest	1s
	4h 18m 33s

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