[proposal] swap out implementation of form with https://github.com/go-playground/form

Hi, I would like to start a discussion,
whether it would make sense to replace https://github.com/ajg/form with https://github.com/go-playground/form.

Why swap:
- go-playground/form has a larger user base/community
- go-playground/form is better tested and vetted
- go-playground/form is tested and used in production environments by many projects
- go-playground/form has a more modern codebase

Why not to swap:
- ajg/form works and has been stable for a long time
- ajg/form has a smaller codebase