Add proper mirror support (#74)

* Add rewrite support and fix existing tests

* Add unit tests for policy matching

* Compile regexes up front and store policies in map

* Add test for verify flow with mirror

* Rename ImageName -> ResolvedName

And only set it when necessary

* Rename Rewrite -> Replacement

but keep it as rewrite in the yaml

test/testdata/local-policy/mapping.yaml

@@ -1,29 +1,18 @@
-# map repos to policies
 version: v1
 kind: policy-mapping
 policies:
-  - origin:
-      domain: docker.io
-      prefix: library/
-    id: test-images
-    description: Local test images
+  - id: docker-official-images
+    description: Docker Official Images
     files:
-      - path: "doi/policy.rego"
-
-mirrors:
-  - policy-id: test-images
-    mirror:
-      domains: ["*"]
-      prefix: "repo"
-  - policy-id: test-images
-    mirror:
-      domains: ["*"]
-      prefix: "library/"
-  - policy-id: test-images
-    mirror:
-      domains: ["*"]
-      prefix: "test-image"
-  - policy-id: test-images
-    mirror:
-      domains: ["*"]
-      prefix: "image-signer-verifier-test"
+      - path: doi/policy.rego
+rules:
+  - pattern: "^docker[.]io/library/(.*)$"
+    policy-id: docker-official-images
+  - pattern: "repo$"
+    policy-id: docker-official-images
+  - pattern: "test-image$"
+    policy-id: docker-official-images
+  - pattern: "image-signer-verifier-test$"
+    policy-id: docker-official-images
+  - pattern: "library/(.*)$"
+    rewrite: docker.io/library/$1