debian: Add watch configuration for uscan

debian: Add watch configuration for uscan

Packages defined as '3.0 (quilt)' are expected to provide information
about how the latest upstream information can be obtained,
as a special d/watch file. This can then get used by uscan(1).

To see how the metadata is utilized, and how the network requests
are made behind the scenes, you can locally run:
$ uscan --no-download --verbose --debug

Resolves: lintian: debian-watch-file-is-missing

Signed-off-by: Valters Jansons <valter.jansons@gmail.com>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>