Helm Chart: Support extra volume mounts

[oWretch]

Proposed changes

Add support for mounting additional volumes into the containers

Problem: We leverage internal certificates for communication between services and need to load the trusted root certificate into the containers. Mounting the certificate as a volume prevents us having to build our own container image.

Solution: Allows providing additional volumes to be mounted into containers, and the volume mounts to enable different combinations to be mounted in addition to the default mounts. If none are provided there is no change in the deployment

Testing: Deploy the chart with and without additional volume mounts.

Closes #1199

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

[kate-osborn]

@oWretch I filed an issue for this PR as well and added it to the PR description: #1199.

I'll take a look at both PRs this week.