[DOC] add init/shutdown documentation

[toddbaert]

Change in the documentation

We need to initialization/shutdown documentation to the evaluation API and provider docs.

It should include:

• provider updates:
  • explanation of initialize/shutdown functions, with code samples
• evaluation API updates:
  • explanation of API shutdown
  • links to events for explaining how to register handlers for PROVIDER_READY/ERROR.

NOTE: we may want to wait for at least one SDK implementation so we can have code examples.