PNG-8 greyscaling to allow rendering on e-ink displays

[devbar]

This feature is very usefull if grafana should render on an eInk display with greyscale only. I use it for a jailbreaked kindle.

This implementation does not allow to pass the greyScaleImage flag in the render url. Maybe some of you can point me to the right line of code. Until this it's necessary to send the arg in the URL of the renderer in docker config.

 grafana:
    [...]
    environment:
      - GF_INSTALL_PLUGINS=grafana-image-renderer
      - GF_RENDERING_SERVER_URL=http://renderer:8081/render?greyScaleImage=true
    [...]

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[Proximyst]

We are currently not accepting new features targetted at the Node.js codebase; feel free to resubmit once the Go rewrite is complete (aka when 5.0.0 is released).