Intermediate docker images for specific HLMs without FATES?

[glemieux]

Is there any benefit to separate out the HLM Dockerfile build from the FATES configuration? At first I was thinking this didn't really make much sense since the last step for integrating FATES is so minor. That said perhaps we could do this so as to create specific HLM-only images with descriptive tags that correlate to a particular HLM version. This separation of steps might simplify the tagging structure given that one commit of fates_next_api can suffice for multiple commits of FATES typically.