chore(enos): Use docker image generated from code (#3100)

Makefile

@@ -325,7 +325,7 @@ REGISTRY_NAME?=docker.io/hashicorp
 IMAGE_NAME=boundary
 VERSION?=0.7.4
 IMAGE_TAG=$(REGISTRY_NAME)/$(IMAGE_NAME):$(VERSION)
-IMAGE_TAG_DEV=$(REGISTRY_NAME)/$(IMAGE_NAME):latest-$(shell git rev-parse --short HEAD)
+IMAGE_TAG_DEV?=$(REGISTRY_NAME)/$(IMAGE_NAME):latest-$(shell git rev-parse --short HEAD)
 
 .PHONY: docker
 docker: docker-build