Augment repo with DRS CV

[durack1]

This repo has not been updated to include the project DRS template, ala https://github.com/WCRP-CMIP/CMIP6_CVs/blob/main/CMIP6_DRS.json. It would be useful to add this, so that CMOR can use this CV by default if not provided in the user_input.json

See chatter in the CMOR repo, planning for CMOR 3.12 - PCMDI/cmor#267 (comment)

[durack1]

Some additional changes will be required to table files in preparation for CMOR 3.12. Let's await the release (likely tomorrow Fri 5 Sep 2025), and then get things working with the update.

@gleckler1 @mauzey1 @sashakames ping