bug: update parameter to online update check is not passed through to increment-downloads API

[mcdurdin]

The update parameter is passed in the URL for /go/download/package on keyman.com but increment-downloads API and backend does not have any place to take or store the data.

This will also be relevant for app-downloads-increment API, where the same issue arises.

See-also: keymanapp/keyman#15433