Generate interfaces for fill-form data

[MichaRedM]

Is your feature request related to a problem? Please describe.
Each fillForm method expects an interfaces, which is defined inline in the method header. This interface is allways copied to have an interface for the matching test-data

Describe the solution you'd like
Is should be possible, to generate the interface, by a given name, which is expected in the fillForm

For example:

await page.addFillForm('IPageFormData');