refactor(configuration): remove agent configs from `configuration` crate

[luketchang]

Should not have agent run-time configuration in the network/contract JSON config files. Also want to be able to more easily override/supply agent config blocks from env.

• want break agent configuration out of configuration such that the agent can take
  • a short JSON file with config data (e.g. just processor block in file)
  • environment variables (can implement from_env() in decl_config!
  • a mix of config file + env variables for overriding config file