feat: enable extra volume mounts for front end

[donbowman]

This allows adding icons to generic events, e.g. add:

  extraVolumeMounts:
    - mountPath: /app/public/icons/eventc-icon.png 
      name: icons 
     subPath: eventc-icon.png 
  extraVolumes:
    - name: icons
      configMap: 
       name: icons
  

to the frontend section (and make a config map with your icon).

I added the icon config map via kustomize:

configMapGenerator:
  - name: icons files: - eventc-icon.png

Closes #

📑 Description

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• My pull request adheres to the code style of this project
• My code requires changes to the documentation
• I have updated the documentation as required
• All the tests have passed

ℹ Additional Information

[talboren]

lgtm