Amend radiation budget slightly to label plots with an alias

[NParsonsMO]

To work with a new climate model evaluation tool at the Met Office, we would like these plots to be labelled with the datasets aliases rather than their dataset name.

This will have the effect of adding "CMIP6_" to the beginning of the datasets names in the plots if the recipe is run in its default configuration, but will enable other names to be used is the user wishes, by adding alias: <intended_name> to the dataset in the recipe.

It also seems neat to remove the dataset-specific description that appears in the recipe.