feat(relay): group-commit batching for plain event inserts (F1) #3043

Job	Run time
Build (linux/arm64)	5m 43s
Build public push gateway (linux/arm64)	2m 39s
Build (linux/amd64)	6m 40s
Build public push gateway (linux/amd64)	3m 2s
Publish public push gateway image	0s
Merge multi-arch manifest	0s
	18m 4s

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