Uploading document from Microsoft Teams

[dmoorjmalani]

Hi - We have 300+ teams created, where people collaborate on Proposals, now. Once the proposal is complete the final proposal document should go to a knowledge repository, which is a separate classic SharePoint site collection. I am looking for a way to automate that, and from the research it seems like, a conversational bot, which would take a few inputs (one of them would be the document) is the only option. Is there any other simpler way. Maybe a custom action on documents tab of Teams, that user can click on once they are ready to upload the document. 

Because we have a lot teams (and they are increasing everyday) writing a flow with "for a selected item" is also not feasible (because it takes site and document library as inputs), and creating that many flows is out of question.  
Please provide suggestions. Thank you!

[#2]

one of the easy and quickest ways will be to put a new tab where you put that Classic SharePoint either as a website or as SharePoint and it will respect the permission.

let's say I am working with Proposal Team 45 > I got the conversation tab and files tab, I will have another tab calling it Knowledge Repository which is the master and the final files goes there...

hope that helps.

[#3]

Thank you for taking the time out!
Adding document tab would normally work, but in my case the documents are associated to Proposals via Lookup, and I have more that 15K proposals, so there is also an issue of List Threshold, so, i have some jquery written on the EditForm.aspx of document library to record the associated Proposal id. And i don't see option to upload document, there is just drag and drop available. And there is also not any option to open up EditForm, just quick edit, which in my case is not helpful.
Also, even if it worked, it would still mean that user is uploading at two places. If uploading at two places is a last resort then i have a spfx webpart created and I can add that to Teams as a SharePoint Page. But still, i want all this to happen with single click, Is there any way to simplify this?