Update ESM4.2 YAML formatting

[singhd789]

Is your feature request related to a problem? Please describe.
Update yaml formatting

In esm4.yaml:

• move directories and postprocess section to own ./pp/settings.yaml for example

• add settings.yaml path under experiment's:

     experiments:
         - name: "ESM4p2_piControl_spinup_J"
           settings: "settings.yaml"
           pp: 
  

• remove shared section

In new pp/settings.yaml:

• in [postprocess][settings]:
  - can add keys: pp_chunks, pp_start, pp_stop, pp_grid_spec if needed/defined
  - for pp_chunks (pp_chunk_a and pp_chunk_b were replaced by pp_chunks)

pp_chunks:
    - *PP_CMIP_CHUNK_A
    - *PP_CMIP_CHUNK_B

• in [postprocess][switches]:
  - remove do_statics
  - add do_analysis_only