Introduce the infrastructure for auto-generating API documentation via sphinx and doxygen #775

Job	Run time
build-and-test (LCG_104/x86_64-el9-gcc13-opt)	8m 48s
build-and-test (dev4/x86_64-ubuntu2004-gcc9-opt)	16m 58s
build-and-test (LCG_104/x86_64-el9-clang16-opt)	6m 27s
	32m 13s

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