refactor(alert): marked fields to be indexable in ES #1307

Job	Run time
style / crystal-style	1m 31s
test / 🚧 crystal: unstable, MT: ☐, canary: ☐	2m 12s
test / crystal: latest, MT: ☐, canary: ☐	2m 25s
test / TODOs → GitHub Issues	-1s
	6m 7s

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