debuginfod: extracted-from-archive file cache

debuginfod: extracted-from-archive file cache

Add a facility to service webapi and dwz/altdebug requests that
resolve to archives via a $TMPDIR file cache.  This permits
instantaneous dwz resolution during -debuginfo rpm scanning, and also
instantanous duplicate webapi requests.  The cache is limited both in
number of entries and in storage space.  Heuristics provide
serviceable defaults.

Signed-off-by: Frank Ch. Eigler <fche@redhat.com>