download_hash.py: generalized and data-driven

The script is currently limited to one hardcoded URL for kubernetes
related binaries, and a fixed set of architectures.

The solution is three-fold:
1. Use an url template dictionary for each download -> this allow to easily
   add support for new downloads.
2. Source the architectures to search from the existing data
3. Enumerate the existing versions in the data and start searching from
   the last one until no newer version is found (newer in the version
   order sense, irrespective of actual age)