Plugins: Require signing of external back-end plugins (#24075)

* PluginManager: Require signing of external plugins

Co-authored-by: Marcus Efraimsson <marcus.efraimsson@gmail.com>
Co-authored-by: Diana Payton <52059945+oddlittlebird@users.noreply.github.com>

pkg/plugins/testdata/invalid-signature/plugin/MANIFEST.txt

@@ -0,0 +1 @@
+Invalid manifest

pkg/plugins/testdata/invalid-signature/plugin/plugin.json

@@ -0,0 +1,14 @@
+{
+  "type": "datasource",
+  "name": "Test",
+  "id": "test",
+  "backend": true,
+  "state": "alpha",
+  "info": {
+    "description": "Test",
+    "author": {
+      "name": "Grafana Labs",
+      "url": "https://grafana.com"
+    }
+  }
+}

pkg/plugins/testdata/unsigned/plugin/plugin.json

@@ -0,0 +1,14 @@
+{
+  "type": "datasource",
+  "name": "Test",
+  "id": "test",
+  "backend": true,
+  "state": "alpha",
+  "info": {
+    "description": "Test",
+    "author": {
+      "name": "Grafana Labs",
+      "url": "https://grafana.com"
+    }
+  }
+}