[source - github] - Add Custom Properties Stream

[cairo-thompsonn]

Our team would love to bring in the GutHub Custom Properties data to our Snowflake destination. We currently do not have the capacity to do it ourselves at the moment so creating an issue in the off chance someone else is in need or is feeling motivated to add it! Here is the API endpoint https://docs.github.com/en/rest/repos/custom-properties?apiVersion=2022-11-28