feat: Allow custom config

[Khaledgarbaya]

Fixes #1718

[emilyemorehouse]

Can you add documentation on what this can be used for and how to use it?

[aidant]

This is something I really look forward to since I frequently run into situations where custom configuration is incredibly helpful. However I suggest we call the property custom rather than customConfig since it adds unneeded content especially when used as config.customConfig.

Edit: I also remember seeing a similar PR however the object was userData.

[yasuf]

This is already fixed and will be released as part of 0.19.1, seehttps://github.com//pull/2207