fix: ECS tries to pull a non-existent image on certain slices

[dtsai-czi]

Related to #238--what is the intended behavior for when slices are built, tagged, and pushed? If none of the services named in the integration secret belong to the profile defined by the slice, it seems that ECS looks to pull an image for a tag that doesn't get pushed and consequently hangs. Would it make sense to just push all services defined in docker-compose just so ECS at least finds something and doesn't hang?

[edulop91]

There is an implicit/undocumented assumption that only services with a build key are actually built and assumed part of a "remote/ecs service". Any docker-compose service without a build key is assumed to be only useful for local development.