Consistent colouring for stacked bar charts with unknown number of series and a dynamic display order

### What happened? We have a lot of stacked bar charts where the stacks are ordered from largest number first. The problem we have is that this means every refresh the colours for a particular series changes, making it hard to monitor over time. It would be nice if we could colour based on the series name (or hash?). We don't know the series in advance, so we can't add name overrides. We order the stacked bars by size, meaning different series can be in the first position on a refresh. One example of a chart: count of errors on services. We have a large (500+?) and growing number of services. The error patterns can be constant or bursty or oscillate. It would be good to be able to look at the chart and think, "It's the orange one causing trouble again, lets take a closer look", but at the moment the orange one doesn't represent a particular service, unless I get someone to provide named overrides for all the services, and add to that list as we build more. ### What did you expect to happen? To be able to specify a field that the colour is based on (e.g. service name), rather than it being based on series order (e.g. service that currently has the most errors) ### Did this work before? No ### How do we reproduce it? 1. Make a bar chart of services ordered by error total 2. 3. ### Is the bug inside a dashboard panel? _No response_ ### Environment (with versions)? Grafana: OS: Browser: ### Grafana platform? None ### Datasource(s)? _No response_