Add POSTPROCESSING_TOOL_NAME to config_component.xml

In order to provide the name of the postprocessing tool that's being used for a case we want to add POSTPROCSSING_TOOL_NAME

Add something like the following to: cime_config/config_component.xml

``` xml

char
CUPiD
case_comp
env_case.xml
Name of the postprocessing tool (for documentation only - DO NOT EDIT)

```

This is in the case_comp group as that has the names of the components and here the name for the coupler/driver.

We talked about doing this in CUPiD and then @jedwards suggested that the definition should be here.

See this comment here:

https://github.com/NCAR/CUPiD/issues/399#issuecomment-4016659831