Feature request: ability to enter a path and see what headers would be applied

[kaganjd]

- Do you want to request a feature or report a bug? Feature request!

Bringing this over from https://community.netlify.com/t/remove-inherited-header-applied-by-splat-path-in-headers/26263/3:

it’d be soooooo good if, after entering the rules and clicking the “Test rules” button you could then enter a path and it’d tell you what headers it’d get

- What is the current behavior?

tells you if the syntax is any good, and tells you what the equivalent netlify.toml versions of the rules would look like