"superuser" option for custom command "adduser"

<img src="data:image/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==" decoding="async" class="lazy" data-src="https://img.shields.io/badge/reflectometry%20Task%20410%20-%20open%20-%20green">

Refs https://code.ornl.gov/sns-hfir-scse/reflectometry/reflectometry/-/issues/410

Description

Now that the database's volume is not removed between redeployment, we have to verify that the superuser account is already stored in the database. If this is the case, do not attempt to create the same superuser account. Instead, do nothing