Allow users to supply arbitrary HTTP headers for requests
Created by: efritz
Closes https://github.com/sourcegraph/src-cli/issues/238.
This threads header values into the HTTP calls to the Sourcegraph instance via envvars such as SRC_HEADER_FOO=BAR
(where Foo: bar
would be the additional header value - note that header names are case insensitive).
This is applied to:
- GraphQL requests
- LSIF uploads
- get-curl commands
- version command
- campagins actions
This is notably to fix a particular customer's issue, which has their instance behind an authenticating proxy that accepts special bearer tokens.