Add support for configuration discovery

Previously OPA configuration for bundle downloading, status reporting, etc. had to be supplied in a configuration file on startup. With these changes, OPA can be configured to download a bundle that generates the OPA configuration. This allows OPA to boot with minimal configuration and dynamically update that configuration on-the-fly making it much easier to manage large deployments of OPAs for different use cases within the same system.

Signed-off-by: Ashutosh Narkar <anarkar4387@gmail.com>