doc: generate llms.txt #3729

Job	Run time
Build slim tarball	2m 18s
aarch64-darwin: with shared libraries	20m 47s
x86_64-linux: with shared libraries	23m 20s
x86_64-darwin: with shared libraries	37m 37s
aarch64-linux: with shared libraries	20m 9s
	1h 44m 11s

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