chore: run e2e tests on PRs against `release` branch #18

Job	Run time
build (slinky.base.Dockerfile, slinky-base)	1m 0s
build (slinky.e2e.Dockerfile, slinky-simapp)	2m 49s
build (slinky.sidecar.prod.Dockerfile, slinky-sidecar)	3m 14s
build (slinky.local.Dockerfile, slinky-testapp)	3m 41s
build (slinky.sidecar.e2e.Dockerfile, slinky-e2e-sidecar)	3m 44s
deploy	0s
	14m 28s

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