Clean up default setting for OCN_CHL_TYPE

[mnlevy1981]

Description of the issue:

For production runs, we want OCN_CHL_TYPE=prognostic if POP is running with the ecosystem tracer. For testing purposes, it would be useful to have a compset modifier to switch back to diagnostic in https://github.com/ESCOMP/POP2-CESM/blob/master/cime_config/config_component.xml#L37..L54

So something like

  <entry id="OCN_CHL_TYPE">
    <type>char</type>
    <valid_values>diagnostic,prognostic</valid_values>
    <default_value>diagnostic</default_value>
    <values>
      <value compset="_POP2%[^_]*ECO">prognostic</value>
      <value compset="_POP2%[^_]*DIAG_CHL">diagnostic</value>
    </values>
    <group>run_component_pop</group>
    <file>env_run.xml</file>
    <desc>
      Determines provenance of surface Chl for radiative penetration,
      computations. This option is used in the POP ecosystem model.
      The default is diagnostic.
    </desc>
  </entry>

and then update G compsets we use in the test suite to be POP2%ECO%DIAG_CHL if we want to keep the tests bit-for-bit.

Version:

• CESM: latest
• POP2: latest (master as of cesm_pop_2_1_20200709)