Support build images (renovate-bot)

Signed-off-by: Nick Slowinski <nick@nick-slowinski.de>

renovate.json

@@ -12,5 +12,17 @@
       ]
     }
   ],
-  "reviewers": ["nick-slowinski.de/Owners"]
+  "reviewers": ["nick-slowinski.de/Owners"],
+  "customManagers": [
+      {
+      "customType": "regex",
+      "fileMatch": [
+        "build.yml"
+      ],
+      "matchStrings": [
+        "\"image\":\\s\"(?<depName>[^:\"]+):(?<currentValue>[^@\"]+)(@(?<currentDigest>sha256:[a-f0-9]+))?\""
+      ],
+      "datasourceTemplate": "docker"
+    }
+  ]
 }