Allow creation of multiple postgres users

Currently this list is hardcoded to create a `postgres` and `crunchy-postgres` (or whatever the project name is). We should enable the creation of more users with a list variable.

Example of the variable in `values.yaml` and it being used in a chart:
[values](https://github.com/bcgov/cas-cif/blob/develop/chart/cas-cif/values-test.yaml#L8)
[template that uses the values list](https://github.com/bcgov/cas-cif/blob/develop/chart/cas-cif/templates/db-post-upgrade-job.yaml#L22)

Compare the linked values example in values-test.yaml with the chart usage in templates/db-post-upgrade-job.yaml, then locate the corresponding hardcoded user list in this repository. The work is done when the chart accepts a list variable for additional users and uses it to create all configured users.

Written by the indexing model from the issue text.