Generate a GCRCatalogs config at the end of make_object_catalog and merge_metacal_cat

[yymao]

The scripts make_object_catalog.py and merge_metacal_cat.py should generate a config file at the end of the run, so that it'll be easier to create pull requests to GCRCatalogs.

To deal with the path (base_dir) in the config file, we can use the path that is passed to script via --output_dir (cf. https://github.com/LSSTDESC/ImageProcessingPipelines/blob/master/workflows/srs/pipe_setups/run_dpdd). Note that for now we need to replace the path before /dpdd/ to a NERSC path.

cc @johannct @EiffL

[katrinheitmann]

@yymao Any thoughts on this? Thanks!

[yymao]

Is it still planed to produce Object Catalogs for Run 3? If so I guess we will still benefit from implementing this feature. If not then I guess this issue is moot.