caddyhttp: Add {?query} placeholder (#6714)

* caddyhttp: Add `{prefixed_query}` placeholder

* fastcgi: Preserve query during canonical redirect

* Use orig_uri instead for the redirect, shorter Caddyfile shortcut

caddytest/integration/caddyfile_adapt/php_fastcgi_matcher.caddyfiletest

@@ -33,7 +33,7 @@ php_fastcgi @test localhost:9000
 																	"handler": "static_response",
 																	"headers": {
 																		"Location": [
-																			"{http.request.orig_uri.path}/"
+																			"{http.request.orig_uri.path}/{http.request.orig_uri.prefixed_query}"
 																		]
 																	},
 																	"status_code": 308