Add GradientEmitter to support OMG-MEGA and OG-MAP-Elites #2083

Job	Run time
coverage	2m 5s
pre-commit	1m 15s
benchmarks	2m 7s
docs	2m 12s
examples	3m 26s
pin	2m 55s
tutorials_list	7s
test (ubuntu-latest, 3.11)	1m 36s
test (macos-latest, 3.11)	5m 27s
test (windows-latest, 3.11)	4m 48s
tutorials (tutorials/arm_repertoire.ipynb)	2m 5s
tutorials (tutorials/cma_mae.ipynb)	2m 38s
tutorials (tutorials/features/example.ipynb)	1m 35s
tutorials (tutorials/fooling_mnist.ipynb)	3m 8s
tutorials (tutorials/lsi_mnist.ipynb)	3m 37s
tutorials (tutorials/lunar_lander.ipynb)	2m 30s
tutorials (tutorials/tom_cruise_dqd.ipynb)	9m 52s
deploy	0s
	51m 23s

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