chore: prepare Realtime for Marketplaces (supabase#49)

* chore: update Packer & Ansible files

Update Packer & Ansible settings to prepare for AWS/DO Marketplaces

* chore: set aws.json's `source_ami` to be user var

`source_ami`'s default is set to x64 Ubuntu 18.04 EBS HVM in
ap-southeast-1 (Singpore), but ami codes change between regions, so this
should be a user variable along with `region`.

* fix: get SECRET_KEY_BASE from env

* chore: proper cleanup of Ansible tmp files

* docs: better error messages for SECRET_KEY_BASE

* ci: fix artifact naming of release assets

fixes supabase#33 and supabase#34

Merge pull request supabase#35 from soedirgo/feature/ci

Automate tests, build, & release

Bumps the release, prepping changelog

Merge branch 'master' of github.com:supabase/realtime

Bumping version for new docker release