This release switches from the bitnami image to the official discourse/discourse
image. Some env vars need to be renamed for this migration; everything else
should happen automatically.

** WARNING A: renaming env vars

Rename these in your app's .env (the values carry over):

  DISCOURSE_SMTP_HOST     --> DISCOURSE_SMTP_ADDRESS
  DISCOURSE_SMTP_USER     --> DISCOURSE_SMTP_USER_NAME
  DISCOURSE_SMTP_AUTH     --> DISCOURSE_SMTP_AUTHENTICATION
  DISCOURSE_SMTP_PROTOCOL --> DISCOURSE_SMTP_ENABLE_START_TLS (takes a boolean true/false, not the old tls/ssl value, so translate it rather than copying it straight across)

** WARNING B: undeploy before deploy 

it is necessary to `abra app undeploy` your old discourse app before deploying this version. otherwise the database will get killed and be in a bad state before the migration. 
this was a non-fatal error in testing, but still a huge pain. 

`abra app undeploy YOURDOMAIN` # cleaning stops your discourse
`abra app deploy YOURDOMAIN` # with the new version 

** WARNING C: install user

if your deployment's database has an "install user" other than `postgres`
(some older deployments do), you must set the POSTGRES_USER env var in your .env
for this migration, otherwise the postgres upgrade aborts with an install-user
mismatch.

Check your old deployment's install user before upgrading (if this command returns postgres, then you do not need to set this env):

  abra app run YOURAPPDOMAIN db -- psql -U discourse -tAc 'select rolname from pg_roles where oid = 10'