Use rebar3 format for aws-erlang

[onno-vos-dev]

rebar3 format is the future nowadays and becoming the industry standard for formatting code. We should follow along and use rebar3 format across the project.

Make use of a .git-blame-ignore-revs file to ignore the formatter commit: https://michaelheap.com/git-ignore-rev/

[onno-vos-dev]

I tried it out and there's a bug in rebar3 format it seems when it comes to dealing with binary comprehensions which we use in aws_util.erl so either we'd have to skip that file for now or wait for a fix of: AdRoll/rebar3_format#342

I'll leave this for some time before seeing if we may want to proceed in the meantime anyway.