* caddyfile: Fix `import` replacing unrelated placeholders
See https://caddy.community/t/snippet-issue-works-outside-snippet/12231
So it turns out that `NewReplacer()` gives a replacer with some global defaults (like `{env.*}` and some system and time placeholders), which is not ideal when running `import` because we just want to replace `{args.*}` only, and nothing else.
* caddyfile: Add test
a8d45277ca