I noticed I can't specify the streams I want in the GitHub connector (for example, I don't want to ingest PR data). 1. Is there any connector that does this? 2. Hypothetically, how would I add an webapp UI option on the source connector onboarding page (If I have a custom connector). For example, for GitHub source connector I can only specify a few options like "start_date". Where do these options get defined?

It shouldn't matter when you set up the source how many streams there are, it's when you configure the destination that you set up what streams are actually ingested. You can use the same source in a lot of different destinations in theory.