Revisit experiment end years (CMIP continuous DECK)

[durack1]

For CMIP6 the historical experiment ends in 2014, whereas for CMIP6Plus historical will likely extend to 2021 when new forcing data collection becomes available (3 of x datasets are now being reviewed), and 2024+ when CMIP7 proper is ready.

Opening this issue to start a dialogue as to how we manage this through a transition.

Note in the cmip6-cmor-tables\CMIP6_CVs.json, the start_year, end_year and min_number_yrs_per_sim are not defined (e.g. historical here), only in the CVs (here).

This will also be relevant for other experiments, e.g. LESFMIP intends to continue to extend some experiment simulations indefinitely into the future as continuing updates to forcing datasets become available

@matthew-mizielinski @wolfiex @taylor13 ping