Add MobileBert to NormalizedConfigManager

[yomidotk]

What does this PR do?

This PR adds MobileBert to the NormalizedConfigManager to help extend ONNX optimization support.

Changes:

• Mapped mobilebert to NormalizedTextConfig in optimum/utils/normalized_config.py.
• Removed mobilebert from the missing configs TODO list.
• Added a test case for mobilebert in TEXT_ENCODER_MODELS within tests/utils/test_dummpy_input_generators.py.

All local tests passed successfully.

Fixes #1272

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you make sure to update the documentation with your changes?
• Did you write any new necessary tests?

Who can review?

@echarlaix @JingyaHuang @michaelbenayoun @IlyasMoutawwakil