Allow port to be configurable

Regex:

- `^`        Line start
- `#*\s*`    Find line even if commented out
- `(port)`   'port' -- capture as backreference `\1`
- `\s*=\s*`  Equals sign, whether or not surrounded by whitespace
- `\d{4,5}`  Existing port value, expected at 4/5 digits
- `(.*)`     Remainder (i.e. comment) -- capture as backreference `\2`
- `$`        Line end

postgres/defaults.yaml

@@ -3,6 +3,7 @@
 postgres:
   use_upstream_repo: True
   version: '9.5'
+  default_port: 5432
   pkg: postgresql
   pkgs_extra: []
   pkg_client: postgresql-client