Developer guidance: ensure all CMEW recipes make use of `alias` as plot labels

Prerequisite: #456

This is pending a decision on plan for developer guidance, specifically for science domain owners / AutoAssess area owners. The current draft guidance is now quite old.

To ensure consistent plot labelling we want all CMEW recipes to make use of the `alias` facets in dataset descriptions. CMEW will include this facet in the dataset descriptions that it inserts into recipes. This will be implemented for radiation budget in #260, but we need to make it a requirement for future recipes used by CMEW.

#299 and #302 will ensure that this happens for the existing recipe, but we need to have developer guidance to ensure that future recipes use `alias` before they are added to CMEW.

Review prerequisite #456 and the current developer-guidance draft first, then compare #260, #299, and #302 for the existing recipe changes. Done means an agreed developer-guidance update requiring future CMEW recipes to use alias facets for plot labels.

Written by the indexing model from the issue text.