Add fields to catalog_info.json

[delucchi-cmu]

Feature request

Add the following fields that are known at import time to the catalog_info.json file. At this time, they are not needed programatically in the Catalog object.

• partition threshold
• sort columns
• importing tool name
• import date

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Please check the following:

• I have described the purpose of the suggested change, specifying what I need the enhancement to accomplish, i.e. what problem it solves.
• I have included any relevant links, screenshots, environment information, and data relevant to implementing the requested feature, as well as pseudocode for how I want to access the new functionality.
• If I have ideas for how the new feature could be implemented, I have provided explanations and/or pseudocode and/or task lists for the steps.

[delucchi-cmu]

With #358, these are possible to set via kwargs. astronomy-commons/hats-import#393 will implement setting the fields on catalog import.