Update colour mapper to work with Grafana 8 or find better way to do fixed colour mapping

[tofu-rocketry]

The structure of the dashbaord JSON has changed and it seems that includes how manual series colours are set. This means that colourmapper.py is unlikely to work without an update. The other possibility is that Grafana 8 has a better way to do a fixed colour mapping, so that should be investigated first.

This needs to be done before #111 can be sorted.