The sticker submission page (https://developer.apple.com/app-store/sticker-submissions/) explains that:
"If you've bundled your sticker pack or your iMessage app with your iOS app, they will share the same product page information. You do not need to provide these details for the App Store for iMessage."
It seems that just including the extension and icons within the app's build is all that is needed. It just feels weird submitting the app without letting iTunes Connect know in any way whatsoever that there is a sticker pack being included. I wouldn't want the app to be approved and the sticker pack not to be listed on the "App Store for iMessage" or for nobody to know that the app download came with a sticker pack included. If there is anything I am missing about submitting an app with sticker pack extension through iTunes Connect - please let me know! Thanks!!