feat: add general synthetic data iterator and examples for WAN and FLUX.

[jianhan-amd]

In the PR, a data iterator for synthetic image/video data is implemented with following features.

• A general synthetic data iterator for all the supported models for quick model testing and benchmark.
• Support to load input dimensions from the model pipeline.
• Support to override input dimensions from the config yaml.
• Examples for WAN and FLUX models are provided.

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[entrpn]

@jianhan-amd thanks for the submission. Can you add unit tests to this workflow. You can add them inside this file.

Then make sure to run ruff check --fix. I'll kick off the tests again once submitted. Thanks!