Allow optionally keeping internal pages in HTML index. #8633

Job	Run time
MacOS (macOS-14)	21m 56s
MacOS (macOS-13)	45m 38s
Windows (installer, arm)	24m 44s
Linux (gcc, debian:testing, arm)	32m 23s
Windows (check, arm)	55m 30s
Windows (check, intel)	50m 44s
Linux (clang, debian:stable, arm)	32m 4s
Windows (installer, intel)	23m 37s
Linux (gcc, debian:testing, intel)	32m 2s
Linux (clang, debian:testing, intel)	33m 35s
Linux (clang, debian:stable, intel)	35m 2s
Linux (gcc, debian:stable, intel)	32m 57s
Linux (gcc, debian:stable, arm)	31m 23s
Linux (clang, debian:testing, arm)	31m 2s
	8h 2m 37s

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