Add GradientEmitter to support OMG-MEGA and OG-MAP-Elites (#348) #2086

Job	Run time
benchmarks	1m 59s
coverage	2m 12s
pin	2m 52s
pre-commit	1m 13s
docs	2m 20s
examples	3m 14s
test (ubuntu-latest, 3.11)	1m 44s
tutorials_list	8s
test (macos-latest, 3.11)	4m 24s
test (windows-latest, 3.11)	4m 57s
tutorials (tutorials/arm_repertoire.ipynb)	1m 25s
tutorials (tutorials/cma_mae.ipynb)	3m 22s
tutorials (tutorials/features/example.ipynb)	1m 12s
tutorials (tutorials/fooling_mnist.ipynb)	3m 17s
tutorials (tutorials/lsi_mnist.ipynb)	4m 0s
tutorials (tutorials/lunar_lander.ipynb)	2m 23s
tutorials (tutorials/tom_cruise_dqd.ipynb)	11m 11s
deploy	0s
	51m 53s

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