fix: split report global keys into raw and computed across plugins

The `<plugin>-global-<property>` keys in `:report` output returned the resolved value with the built-in default substituted in, so external tooling could not distinguish a property that had been set globally to the default from one that had never been set. The bare keys for caddy, haproxy, and traefik global-only properties had the same shape. The `global-<property>` keys now hold the raw stored value and are empty when nothing has been set, and a new `computed-<property>` key holds the effective value used at runtime, falling back through the per-app value (where one exists), the global value, and the built-in default. The bare global-only keys for the three proxy plugins are removed in favor of the raw/computed pair. Closes #8631.

tests/unit/builder-dockerfile.bats

@@ -46,7 +46,7 @@ teardown() {
   echo "output: $output"
   echo "status: $status"
   assert_success
-  assert_output "Dockerfile"
+  assert_output ""
 
   run /bin/bash -c "dokku builder-dockerfile:report --global --format json | jq -r 'has(\"dockerfile-path\")'"
   echo "output: $output"
@@ -64,7 +64,23 @@ teardown() {
   echo "output: $output"
   echo "status: $status"
   assert_success
-  assert_output "Dockerfile"
+  assert_output ""
+
+  run /bin/bash -c "dokku builder-dockerfile:set --global dockerfile-path Dockerfile.custom"
+  echo "output: $output"
+  echo "status: $status"
+  assert_success
+
+  run /bin/bash -c "dokku builder-dockerfile:report --global --builder-dockerfile-global-dockerfile-path"
+  echo "output: $output"
+  echo "status: $status"
+  assert_success
+  assert_output "Dockerfile.custom"
+
+  run /bin/bash -c "dokku builder-dockerfile:set --global dockerfile-path"
+  echo "output: $output"
+  echo "status: $status"
+  assert_success
 }
 
 @test "(builder-dockerfile:set)" {