Make HTTP header not use underscore

Usually it's fine, however we observed many cases that when users put pinot controller/brokers behind a nginx reverse proxy, then it will by default drop headers with underscore.

For now at least we should put header with both underscore and hyphen.

Sample headers causing problem: `DOWNLOAD_URI` and `UPLOAD_TYPE` in segment upload.

The temporary fix comes from nginx directly, users need to explicitly set `underscores_in_headers on;`
ref: https://www.nginx.com/resources/wiki/start/topics/tutorials/config_pitfalls/#missing-disappearing-http-headers

cc: @zhtaoxiang @npawar @mayankshriv

Start by searching the segment upload handling for the DOWNLOAD_URI and UPLOAD_TYPE headers. Check how those headers are emitted and verify that clients behind nginx can receive both underscore and hyphen forms without requiring underscores_in_headers; add or update the relevant request/response test if one is found nearby.

Written by the indexing model from the issue text.