Add a resubmit argument to SubmitReference.submit

[RvPr]

SubmitReference.submit currently has resubmit hard-coded to false. This prevents submitting links that were previously submitted in the past. It would be helpful to make this a configurable option.

This is identical to the feature added recently in PRAW.

I have no experience with Kotlin or the frameworks being used in this project. But if we are in agreement about the feature, I can submit a pull request that attempts to implement it.