fix(command-dev): serve static file if exists for non forced redirects

[erezrokah]

- Summary

Fixes #1299
Fixes #1221

This worked and served a.html instead of rewriting if a.html existed

[[redirects]]
from = "/a"
status = 200
to = "/docs/a"

This didn't (default status is 301) and always redirected even if a.html existed

[[redirects]]
from = "/a"
to = "/docs/a"

See more here about file shadowing

- Test plan

Added a test

- A picture of a cute animal (not mandatory but encouraged)