In fact, the repository is open for pull requests and you can create on via forking the repository first. But if you look at the open PRs from other non-Atlassians (for example this one from 2017 or this one from 2018) chances are you're not gonna get yours merged unfortunately. :(
One more general tip though, for app development related questions the Atlassian Developer Community / CDAC is the better place to go, instead of the more user focused Atlassian Community. :)
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