Adding region & table(s) envvar overrides

[awinder]

I was tracking the discussion in #27 and took a crack at starting to allow for lambda environment overrides. Region & table subset support was pretty easy, but the configuration files around scaling strategies are pretty verbose. Not sure yet about the best possibilities here, but it might make sense to have a simpler strategy that takes some solid guesses but limits the amount of config decisions to make. Figured this was straightforward enough as a start and happy to put more work in / have a conversation around where you'd like to see this go 😄

[tmitchel2]

Environment variables is definitely the way to go here but I need to think what the strategic end state should look like and setup a plan.... ill try and get around to this in the coming weeks.