Add periodic hamiltonian learning example #392

Job	Run time
setup	2s
generate-example (heat-capacity)	2m 6s
generate-example (batch-cp2k)	1m 59s
generate-example (periodic-hamiltonian)	7m 11s
generate-example (sample-selection)	3m 29s
generate-example (path-integrals)	1m 48s
generate-example (dos-align)	6m 8s
generate-example (gaas-map)	4m 4s
generate-example (pi-metad)	4m 5s
generate-example (roy-gch)	3m 19s
generate-example (lode-linear)	3m 16s
generate-example (lpr)	3m 21s
build-and-publish	33s
	41m 21s

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