Add ssp126 imsi

Initial stab at defining SSP126 and SSP126-extension experiment in imsi (for CP4C/cp4c-docs#2 (closed))

Notes

• ssp126 and the extension are the same experiment_id in CMIP6 parlance. Therefore, this has been used here. However, two imsi experiments are defined (cmip6-ssp126 and cmip6-ssp126-ext). This is necessary because the settings differ between these runs. Both are defined to have the same experiment_id though (for metadata purposes and following the CMIP6 CV definitions).

To before merging:

• Verify internal runs
• Move across relevant forcing files
• Run tests on niagara

Testing:

See CP4C/cp4c-docs#2 (closed) for comprehensive testing on ECCC-U2 and Niagara.

Affected submodules

• Only alters imsi-config in canesm