Use C12 for atmosphere Tier1 tests

[Dooruk]

Currently Tier1 tests are using C90 resolution which takes about half an hour to complete and requires multiple compute nodes. @rtodling created some low-res backgrounds in the R2D2 folder that we could use.

Afterwards, we could just simply copy tier1 C90 tests to tier2 and users still can access them.

[Dooruk]

This works for 2021 by just making two changes in the tier1 YAML.

[Dooruk]

I'm able to run low resolution atmosphere tests (c13 as opposed to c91).

Following the discussion during last development meeting, we want Swell defaults to be Tier 2 with higher/proper model resolutions. Which is fine, but this will impact the CI-workflow scripting which use tier1 defaults (more like defaults + tier1 overrides). I think as a next step we could see if we can use @ashiklom's swell t1test ufo_testing scripting within the CI-workflow YAMLs.