Add standard-compliant route to serve outdated R packages (#32783) (#32789)

Backport #32783 by Sebastian-T-T

The R package repository currently does not have support for older
versions of packages which should be stored in a separate /Archive
router. This PR remedies that by adding a new path router.

Fixes #32782

Co-authored-by: Sebastian T. T. <109338575+Sebastian-T-T@users.noreply.github.com>

routers/api/packages/api.go

@@ -314,6 +314,7 @@ func CommonRoutes() *web.Route {
 					r.Get("/PACKAGES", cran.EnumerateSourcePackages)
 					r.Get("/PACKAGES{format}", cran.EnumerateSourcePackages)
 					r.Get("/{filename}", cran.DownloadSourcePackageFile)
+					r.Get("/Archive/{packagename}/{filename}", cran.DownloadSourcePackageFile)
 				})
 				r.Put("", reqPackageAccess(perm.AccessModeWrite), cran.UploadSourcePackageFile)
 			})