feat: improve configuration - #169

This PR is to refine the configuration system for Function Stream. Now, the configuration system for Function Stream is finally established. It can support various file formats, including YAML and JSON, and even read configurations from environment variables. This will be significantly beneficial when we operate Function Stream on Kubernetes in the future.

Preview

The configuration will look like:

listen_addr: ":7300"
tube_factory:
  pulsar:
    type: "pulsar"
    config:
      pulsar_url: "pulsar://localhost:6650"
  memory:
    Type: "memory"
  default:
    ref: "pulsar"
runtime_factory:
  wasm:
    type: "wasm"
  default:
    ref: "wasm"