deprecate load_embedded_policy

[lukehinds]

Currently the code carries inbuilt policy at data/policy.json

This is not included by default, a client has to call load_embedded_policy()

However, we should could libraries free from all policy opinions, and instead let the client determine what they need. I therefore propose we add a deprecate message when load_embedded_policy() is called. Should anyone want to use or continue using policy.json, they can import directly in their client implementation.