Nodes hub to store and reuse commonly used node

[haixuanTao]

This PR creates a node hub to store commonly used nodes so that we can make it extremely easy for people to get started with dora.

[Hennzau]

I'm currently working on this PR on the latest version of Dora (0.3.5), so I bumped it from rc0 to release.

Structure

• [x] node-hub folder containing usefuls nodes:
  • [x] dora-record
  • [x] dora-rerun
  • [x] opencv-video-capture
  • [x] opencv-plot
  • [x] ultralytics-yolo

Each python node respects the following structure:

node-hub/
└── node/
    ├── main.py
    ├── README.mdr
    └── pyproject.toml

The pyproject.toml can be installed with pip (pip install node-hub/node), it installs all dependencies and setup a script to directly execute the node from a python env:

  - id: object-detection
    build: pip install ../../node-hub/ultralytics-yolo
    path: ultralytics-yolo

Usage

cd examples/python-dataflow
dora build ./dataflow.yml (or dora build ./dataflow_dynamic.yml)
dora up
dora start ./dataflow.yml (or dora start ./dataflow_dynamic.yml)

Note: if you're running the dynamic dataflow, you will need to start manually the ultralytics-yolo node:

# activate your virtual environment in another terminal
python ultralytics-yolo --name object-detection --model yolov5n.pt