Add catalog JSON terminus to improve performance.

This adds a JSON backed catalog terminus, so that the catalog cache can
migrate away from YAML to a faster and more stable storage format.

This is not the default: that still falls to old, trustable YAML which we know
to be stable and effective.

To enable this, edit your routes.yaml file and add:

agent:
  catalog:
    cache: json

Signed-off-by: Daniel Pittman <daniel@puppetlabs.com>