pgbouncer default password / secret?

[stanvv]

We have a setup with pgbouncer enabled.
pgbouncer: enabled: true
We try to setup the pgbouncer exporter from prometheus community: https://artifacthub.io/packages/helm/prometheus-community/prometheus-pgbouncer-exporter

To setup the connection string, we need a username and a password. I tried to use the default "pgbouncer" user (which by default is the only user with permissions on the pgbouncer database), but could not find the password.
For now I've manually fixed it by granting a manually created user access to the pgbouncer database (grant all privileges on database pgbouncer to mycustomuser@mypostgreqldatabase;) and manually adding that same user as admin_user to pgbouncer.ini in the pgbouncer pod.
But obviously that's a mess to setup in code eventually.

Therefore two questions:

1. Where can we find or set the password for the pgbouncer user?
2. If not available, what is the best way to grant a different user permissions to the pgbouncer database, so we can use it to authenticate with the exporter chart?
   2a: I cannot find a way to add admin_users to pgbouncer.ini via helm values.
   2b: I cannot find a way to edit the auth_file (/home/pgbouncer/users.txt) before deployment