add workflow to add new issues to the project

[barneyb]

Projects can only auto-adopt new issues from a single repo. The client is already using that slot, so add an action to this repo to do the same. Looks like PRs are also added, though they're also considered issues in some ways, so might be free.

I believe updating the project task for changes to the issue/PR status will happen for free, once the project linkage is established.