renovate: track yt-dlp version from dockerfiles

renovate.json

@@ -1,3 +1,18 @@
 {
-  "$schema": "https://docs.renovatebot.com/renovate-schema.json"
-}
+  "$schema": "https://docs.renovatebot.com/renovate-schema.json",
+  "customManagers": [
+    {
+      "description": "Update yt-dlp version in Dockerfiles",
+      "customType": "regex",
+      "managerFilePatterns": [
+        "/^Dockerfile$/"
+      ],
+      "matchStrings": [
+        "ARG YT_DLP_VERSION=\"(?<currentValue>.*?)\""
+      ],
+      "datasourceTemplate": "github-tags",
+      "depNameTemplate": "yt-dlp/yt-dlp",
+      "versioningTemplate": "regex:^(?<major>\\d{4})\\.(?<minor>\\d{2})\\.(?<patch>\\d{2})$"
+    }
+  ]
+}