[proposal] config file versioning

[mirceanis]

In daf 7, the cli has an option of instantiating an agent based on a config yml file.
There should be a versioning scheme processed by the config parser to allow iteration of the configuration syntax.

It could be as simple as a top level entry:

version: "1.0"

or, nested under a known static entry that signals that this is a daf config:

daf-config:
  version: "1.0"

It is unclear at this point how the parser handles older/newer versions of what it can parse.