Yaml_load overwrites previous experiment yamls when multiple experiment yamls are listed in the pp section of the main yaml

[uwagura]

Describe the bug
If multiple experiment yamls are listed in the pp section of the main yaml, then only the last listed yaml will be included in the combined yaml. Any other yamls will be overwritten

To Reproduce
Include multiple experiment yamls within a single experiment in the main yaml, like so:

experiments:
    - name: "CEFI_NWA12_COBALT_V1"
      pp:
          - "yaml_include/MOM6_postprocess.yaml" 
          - "yaml_include/Cobalt_postprocess.yaml"

Expected behavior
Ideally, it would be nice to have the components listed in each experiment yaml included in the combined yaml produced afterwards

Additional context
This problem seems to be caused by each of the experiment yamls containing the same keys. In the example listed above, MOM6_postprocess.yaml and Cobalt_postprocess.yaml each contain the following format

postprocess:
    components:
          - <components here> 

When these two yamls are combined with the main yaml, the combined yaml ends up with two postprocessing keys. When the yaml_load function reads these keys, it will overwrite the first postprocess section with the second one, causing the final file to have only the postprocessing components from the second experiment.

This issue could eventually be fixed by a solution to #161