Hello,

There appear to exist use cases that intend to simply check for the
existence of content in a debuginfod server, without actually
downloading it.  In HTTP land, the HEAD operation is the natural
expression of this.
Instead of implementing a HEAD/describe option, allow users, with enough
verbosity, to print the HTTP response headers upon retrieving a file.
E.g output:

HTTP/1.1 200 OK
Connection: Keep-Alive
Content-Length: 2428240
Cache-Control: public
Last-Modified: Sat, 15 May 2021 20:49:51 GMT
Content-Type: application/octet-stream
Date: Tue, 03 Aug 2021 18:50:36 GMT

Note: the new test is mostly compatible with the nsanci/test-fix
commit. When nsanci/test-fix merges with master I can resubmit the
patch with the test properly rebased and adjusted for maximum
efficiency.

The HEAD functionality will (likely) be put into a new PR for existing checking.

-Noah Sanci