codeintel: Simplify LSIF upload proxy
Created by: efritz
Remove the lsifserver-client Upload
method and instead have the LSIF upload endpoint perform a raw request to the backend.
This is going to simplify the effort in https://github.com/sourcegraph/sourcegraph/pull/10456 as it introduces a handful of new query parameters which would otherwise need to be threaded through to this call.
In order to keep backwards compatibility, we have the api-server (both Go and TypeScript, for now) return string identifiers instead of integers. Previously this conversion was done in the proxy. This behavior is necessary to retain back-compat with src-cli.