Fix code scanning alert - Use of a broken or weak cryptographic hashing algorithm on sensitive data

[taurus-forever]

Tracking issue for:

• https://github.com/canonical/pgbouncer-k8s-operator/security/code-scanning/1

[syncronize-issues-to-jira]

Thank you for reporting us your feedback!

The internal ticket has been created: https://warthogs.atlassian.net/browse/DPE-5336.

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[taurus-forever]

WIP in #313