Add text classification (query intent classification) demo

[xwli-chelsea]

Description

Adding a text classification demo to show how users can train a DeText model from data preprocessing to model inference with a public dataset on query intent classification.

Fixes # (issue) https://github.com/linkedin/detext/issues/33, https://github.com/linkedin/detext/issues/39, https://github.com/linkedin/detext/issues/47

Type of change

Please delete options that are not relevant.

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

List all changes

Added the demo notebook with colab link

Testing

Tested with latest version of DeText in Google colab.

Test Configuration:

• Firmware version:
• Hardware:
• Toolchain:
• SDK:

Checklist

• [ ] My code follows the style guidelines of this project
• [ ] I have performed a self-review of my own code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [ ] My changes generate no new warnings
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] New and existing unit tests pass locally with my changes
• [ ] Any dependent changes have been merged and published in downstream modules