… that matches the major postgres version being upgraded from.

If no package dir exists, because they are making a large upgrade jump, print an error and exit.

…ata directories exist,

print an error and exit.

We no longer have the postgres 9 packages to be able to upgrade from these versions. Users will
have to upgrade to an older first first.

- The changes from tust to peer and md5 are a better security posture, but they break a lot of existing use cases
  and should probably instead be gated behind some sort of configuration flag. Co-located bbr relies upon passwordless
  connection to the database as vcap user, but runs a root. Many of the acceptance tests also try using the vcap user
  but run as root via ssh and fail with the changes.
- Postgres 15 no longer grants users access to the public schema. This prevents generated users from being able to create
  tables. Update the create_databases function to grant access to the public schema for each role on each database.