[FR] Add remaining models from TF2 object detection model zoo

Currently, FiftyOne only contains CenterNet 512x512 with the Hourglass104 backbone from the TF2 model zoo: https://github.com/tensorflow/models/blob/archive/research/object_detection/g3doc/tf2_detection_zoo.md

Other models can be added by updating fiftyone/zoo/models/manifest-tf.json to add relevant information for the new models following centernet-hg104-512-coco-tf2.

It can then be tested with:

conda create -n fo
conda activate fo
conda install tensorflow-gpu=2.2.0
conda install ipython

git clone https://github.com/voxel51/fiftyone.git
cd fiftyone
bash install.bash
eta install models

# Add new models

import fiftyone as fo
import fiftyone.zoo as foz

dataset, session = fo.quickstart()

model = foz.load_zoo_model("NEW_MODEL_NAME", error_level=1)

dataset.apply_model(model, label_field="predictions")

session = fo.launch_app(dataset)