Review start/end_year for all defined experiment_id entries

[durack1]

There may be some inconsistencies in the start/end_year pairs along with the minimum number of years of simulation required.

Implement checks to validate existing entries

[durack1]

The list of potential issues to be reviewed are contained in CMIP6_CVs/src/writeJson.py. These include experiments from the MIPs: CFMIP, DCPP, C4MIP/CDRMIP, FAFMIP, PAMIP, ISMIP6, GeoMIP