Split loading config vs homeserver `setup` (#18933) #1595

Job	Run time
Build and push image for linux/amd64	2m 32s
Build and push image for linux/arm64	2m 23s
Push merged images to ghcr.io/element-hq/synapse	21s
Push merged images to docker.io/matrixdotorg/synapse	23s
	5m 39s

Provide feedback