Implement RFC 104: Adding a "gdal" front-end command line interface #6967

Job	Run time
build-linux-ubuntu-focal	1h 18m 24s
build-mac	9m 26s
build-windows-conda	30m 37s
build-windows-conda-csharp-only	0s
build-windows-minimum	32m 24s
build-windows-msys2-mingw	13m 28s
	2h 44m 19s

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