refactor(setup-db): to run trivy in docker (#54)

As part of our safety initiative, I'm refactoring setup-db to run trivy inside a Docker container with minimal privileges, reducing leakage of secrets, files, etc. to a minimum in case the dependency gets compromised.
Additionally, we are always pinning the trivy docker image to a fixed digest. Renovate has been configured to keep the Trivy image version up-to-date.

Reviewed-on: #54
Reviewed-by: branch-buddy <branch-buddy@t00n.de>
Co-authored-by: Timo Behrendt <t.behrendt@t00n.de>
Co-committed-by: Timo Behrendt <t.behrendt@t00n.de>

renovate.json

@@ -4,6 +4,17 @@
     "local>t.behrendt/renovate-configs:common",
     "local>t.behrendt/renovate-configs:action"
   ],
+  "customManagers": [
+    {
+      "customType": "regex",
+      "description": "Update Trivy docker image",
+      "managerFilePatterns": ["/(^|/)setup-db/action\\.ya?ml$/"],
+      "datasourceTemplate": "docker",
+      "matchStrings": [
+        "default:\\s*\"(?<depName>ghcr\\.io/aquasecurity/trivy):(?<currentValue>[\\d\\.]+)(?:@(?<currentDigest>sha256:[a-f0-9]+))?\""
+      ]
+    }
+  ],
   "packageRules": [
     {
       "matchManagers": ["dockerfile", "kubernetes", "helmfile", "helm-values"],