Revised Opportunity template for Unharmonised DR

[JamesAnstey]

Replaces #212 with simplified templates for adding Opportunities and (if needed) Experiment and Variable Groups.

Opportunity template (yaml file) is here.

Also brought in #204 updates to allow users to produce json or csv files with customized list of variables.

Usage examples in README_unharmonised_workflow.md

TODO:

• Validate experiment names against esgvoc (i.e., assume any new experiments have been registered in CVs)
• Tool to create of variable group yaml file from an edited json file
• As above but for csv file input
• DR API updates to combine Harmonised and Unharmonised requests (where not already addressed in Add possibility to deal with several requests #216)
• Decide where content of Unharmonised requests should be kept (probably not in this software repo or the existing DR Content repo that holds the Harmonised request)

Update: following TISG discussion (15 Sep 2026) a proposed repo structure for the Unharmonised is here:

https://github.com/CMIP-Data-Request/CMIP7_DReq_Unharmonised

with draft of workflow description here:

https://github.com/CMIP-Data-Request/CMIP7_DReq_Unharmonised/blob/main/README_workflow.md

@bethdingley @chloemackallah @martinjuckes