add formdata

[hatch01]

Proposed changes

Add the ability to send FormData encoded data

Type of changes

Adding a new feature.

Put an x in the boxes that apply.

• Bugfix (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)

Checklist

• I have read the CONTRIBUTING doc
• My code follows the Dart coding convention
• Lint and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works.
• I have commented my code, particularly in hard-to-understand areas
• I have added necessary documentation (if appropriate)