Add Renovate regex manager for Docker image tags

renovate.json

@@ -2,5 +2,28 @@
   "$schema": "https://docs.renovatebot.com/renovate-schema.json",
   "extends": [
     "config:recommended"
+  ],
+  "regexManagers": [
+    {
+      "fileMatch": ["(^|/)compose[^/]*\\.yml$"],
+      "matchStrings": [
+        "image:\\s*\"wordpress:(?<currentValue>[^\"]+)\"",
+        "image:\\s*\"mariadb:(?<currentValue>[^\"]+)\""
+      ],
+      "datasourceTemplate": "docker",
+      "lookupNameTemplate": "{{{packageName}}}"
+    }
+  ],
+  "packageRules": [
+    {
+      "matchDatasources": ["docker"],
+      "matchPackageNames": ["wordpress"],
+      "enabled": true
+    },
+    {
+      "matchDatasources": ["docker"],
+      "matchPackageNames": ["mariadb"],
+      "enabled": true
+    }
   ]
 }