feat: split out docker build #441

Job	Run time
Build, stable, linux/arm64	16m 27s
Build, stable, linux/amd64	2m 54s
Trivy Container Scan	2m 29s
Test basic, stable	3m 37s
Anchore Container Scan	1m 46s
Test split, stable	2m 57s
Test SAML, stable	2m 29s
Test novolume, stable	3m 23s
Test single celery process, stable	2m 48s
Test SSL, stable	2m 25s
Merge images	13s
Publish to GitHub, stable	0s
Publish to Docker Hub, stable	0s
Create release on GitHub	0s
	41m 28s

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