Create YOLOX-Tiny and Nano Configs

[zghera]

Task Description

Create the configs for YOLOX-Tiny and YOLOX-Nano.

Create a branch off yolox_4 and create the configs in tf-models/official/vision/beta/projects/yolo/configs/experiments/yolovx/detection/.

The config that we want to base Tiny and Nano on is yolovx_decoupled_head_tpu_e1.yaml.

Before opening a pull request:

• Make sure your configs follow the same style as the other YOLOX configs.
• Build YOLOX-Tiny and YOLOX-Nano models and validate that the number of parameters is correct.