feat(hub): add git clone persistence option #268

Job	Run time
Detect Changes	9s
Build Hub Image	2m 49s
Build Base GPU Image (${{ matrix.gpu_target }})	0s
Build Base CPU Image	0s
Build Code CPU Image	0s
Build Course: ${{ matrix.course }} (${{ matrix.gpu_target }})	0s
Build Code GPU Image (${{ matrix.gpu_target }})	-1s
	2m 57s

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