[imio/helm-plausible-analytics] allow setting additional volumes and their mounts

[vittoriocanilli]

Is your feature request related to a problem? Please describe.
I am creating my secret with all environment variables (used in the secret.existingSecret value) with Secret provider class for Azure Key vaults, which requires an additional volume in the deployment with a specific path. I am using the version 0.4.0 of this chart, where I can not define such volume: therefore the secret provider class cannot create the corresponding secret.

Describe the solution you'd like
I would need new values that allow to create additional volumes and their mounts like this:

volumes: []
# - name: my_volume
#   secret:
#     secretName: my_secret
#     optional: false

volumeMounts: []
# - name: mounted_secret
#   mountPath: "/etc/mounted_secret"
#   readOnly: true

Describe alternatives you've considered
At the moment I am creating the secret manually locally and I apply it: it works, but it is quite cumbersome.

Additional context
I noticed another issue which would benefit by having the chance to define additional volumes and their mounts: #12

[alexnuttinck]

Hello @vittoriocanilli,

I understand the need, this feature request cloud be interesting, thanks.
I am open to review a PR if you want to implement it.

[vittoriocanilli]

Hello @alexnuttinck,

thanks for your answer! I am not very familiar with developing Helm charts, but I could open a PR in the future. For the moment I keep the issue here, in case somebody else is available to work on it.

[vittoriocanilli]

Hello @alexnuttinck,

I have just opened a PR for this issue: #29

Looking forward to get some feedback!