feat: implement pull secrets in helm chart

[mars64]

Supports the use of imagePullSecrets in deployment and serviceAccount objects. Useful for things like authenticating to DockerHub in systems that would otherwise hit pull limits.

This would close #191

Please note: I bypassed the pre-commit hooks as I did not change any of the Java code and am not currently set up with the required local Gradle toolchain. Apologies in advance.