21901: Log all keep-web GET requests that request the first byte

21901: Log all keep-web GET requests that request the first byte

We use this as a heuristic for "starting a new download." This heuristic
does mean that a GET request can avoid being logged if:

* it comes from the same source address (from the server's perspective)
* it uses the same API token
* it requests Range: bytes=1-

Those conditions seem acceptably narrow for now.

The http_range module used here is effectively a public export of the
same logic used by Go's HTTP FS server. I felt like it was important to
use the same logic to avoid different outcomes in the logging logic
vs. serving logic.

Arvados-DCO-1.1-Signed-off-by: Brett Smith <brett.smith@curii.com>