codeintel: Add scheme to frontend URL in indexer
Created by: efritz
Dotcom is seeing a lot of errors like
Post sourcegraph-frontend-internal/.api/lsif/upload?commit=6a8421bcff44c2a9889075724070baaebf8dcd72&indexerName=lsif-go&repository=github.com%2Frobfig%2Fcron: unsupported protocol scheme ""+
because the SRC_FRONTEND_URL is a host/port pair only.