Add resource-types registry for domainId type segment

Mirrors the provider registry pattern in schemas/registry/providers.json,
giving SDKs a governed enum to validate the type segment of domainId
URIs against.

Signed-off-by: xibz <bjp@apple.com>

Author: xibz

schemas/registry/resource-types.json

@@ -0,0 +1,63 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "https://cdevents.dev/0.6.0-draft/schema/links/resource-types",
+  "description": "Registry of known CDEvents domainId resource type identifiers. Known resource types are listed below. To register a new resource type, submit a pull request adding an entry below and to the Common Resource Types table in links.md.",
+  "type": "string",
+  "pattern": "^[a-z][a-z0-9-]*(\\.[a-z][a-z0-9-]*)*$",
+  "oneOf": [
+    {
+      "const": "pr",
+      "description": "A pull or merge request",
+      "examples": ["42"]
+    },
+    {
+      "const": "commit",
+      "description": "A source code commit",
+      "examples": ["abc123def456"]
+    },
+    {
+      "const": "issue",
+      "description": "An issue or ticket in a tracking system",
+      "examples": ["1234"]
+    },
+    {
+      "const": "branch",
+      "description": "A source code branch",
+      "examples": ["main", "feature/my-branch"]
+    },
+    {
+      "const": "tag",
+      "description": "A source code tag or release",
+      "examples": ["v1.2.3"]
+    },
+    {
+      "const": "definition",
+      "description": "Abstract parent. MUST NOT be used directly — use a concrete subtype."
+    },
+    {
+      "const": "definition.workflow",
+      "description": "An automation or pipeline definition — any template that describes a sequence of steps to be executed (e.g. a GitHub Actions workflow file, a CircleCI pipeline config, a Jenkinsfile).",
+      "examples": [".github%2Fworkflows%2Fci.yml"]
+    },
+    {
+      "const": "execution",
+      "description": "A top-level run of a pipeline, workflow, or build. Always refers to the top-level execution — stages, jobs, and steps are out of scope.",
+      "examples": ["789"]
+    },
+    {
+      "const": "artifact",
+      "description": "A build artifact (binary, container image, package, etc.). The resource id SHOULD be a PURL (https://github.com/package-url/purl-spec), URL-encoded.",
+      "examples": ["pkg%3Adocker%2Fmyapp%401.0.0"]
+    },
+    {
+      "const": "environment",
+      "description": "A target deployment environment",
+      "examples": ["production", "staging"]
+    },
+    {
+      "const": "alert",
+      "description": "A monitoring or observability alert",
+      "examples": ["98765"]
+    }
+  ]
+}