Define project-wide labelling conventions

[EllieKallmier]

Is your feature request related to a problem? Please describe.
I don't want to end up with disparate labelling systems across multiple repos in the same project if we can avoid it. This would just add avoidable complexity and prevent strong linkage across repos.

Describe the solution you'd like
I think we could benefit from setting out a simple syntax for issue and PR labelling across repos, e.g. using [keyword] : [descriptor] for all labels. Defining a set of standard labels to use everywhere and then some more context-specific options would be useful too.

Describe alternatives you've considered

• Different schemas for labelling?
• Applying the "Issue Type" field at the organisation level (maybe also?)
• Using issue/PR naming to hold some of the label info instead

[EllieKallmier]

• Happy to try out [keyword] : [desc] structure
  • For the moment - stick with “category” and “type”
  • Consider adding “domain” (to refer to e.g. storage, generators, something more specific to the content from modelling perspective) in future

TODO: document these decisions more formally and add as docs to dev-practices repo

[EllieKallmier]

Also TODO: set up the labels in other repos according to the [keyword] : [description] structure