Allow overrides in install-bootstrap-creds.sh

Allows for for credential variables to be overridden during the
bootstrapping process on certain install methods (i.e. for
development purposes and OLM). These variables include:

- `PGOADMIN_USERNAME`
- `PGOADMIN_PASSWORD`
- `PGOADMIN_ROLENAME`

Author: sathieu

deploy/install-bootstrap-creds.sh

@@ -17,9 +17,9 @@ set -eu
 
 # fill out these variables if you want to change the
 # default pgo bootstrap user and role
-PGOADMIN_USERNAME=admin
-PGOADMIN_PASSWORD=examplepassword
-PGOADMIN_ROLENAME=pgoadmin
+PGOADMIN_USERNAME="${PGOADMIN_USERNAME:-admin}"
+PGOADMIN_PASSWORD="${PGOADMIN_PASSWORD:-examplepassword}"
+PGOADMIN_ROLENAME="${PGOADMIN_ROLENAME:-pgoadmin}"
 PGOADMIN_PERMS="*"