Add platform filtering support to mapping.yml (#167)

* chore!: rename package config -> mapping
* feat: add platform filtering support to mapping.yml

mapping/testdata/mappings/doi-platform/mapping.yaml

@@ -0,0 +1,17 @@
+version: v1
+kind: policy-mapping
+policies:
+  - id: docker-official-images
+    description: Docker Official Images
+    files:
+      - path: doi/policy.rego
+rules:
+  - pattern: "^docker[.]io/library/(.*)$"
+    platforms: ["linux/amd64"]
+    policy-id: docker-official-images
+  - pattern: "^docker.io/mozilla/(.*)$"
+    platforms: ["linux/amd64", "linux/arm64"]
+    policy-id: docker-official-images
+  - pattern: "^mycoolmirror[.]org/library/(.*)$"
+    platforms: ["linux/amd64"]
+    rewrite: "docker.io/library/$1"