Support cpp/deps.txt

Our cpp projects use deps.txt to list and download their dependencies.
These should be automatically updated.

This is especially important because floating dependencies may break the
build when we don't expect it to. E.g: cucumber/gherkin#206

cpp-deps-txt.json

@@ -0,0 +1,16 @@
+{
+  "$schema": "https://docs.renovatebot.com/renovate-schema.json",
+  "description": "Parse cpp/deps.txt files",
+  "regexManagers": [
+    {
+      "fileMatch": [
+        "(^|/)deps\\.txt"
+      ],
+      "matchStrings": [
+        "https://github.com/(?<depName>.*?)/archive/refs/tags/(?<currentValue>.*?).zip"
+      ],
+      "datasourceTemplate": "github-tags",
+      "versioningTemplate": "semver"
+    }
+  ]
+}

default.json

@@ -8,7 +8,8 @@
     ":automergeBranch",
     ":automergeMinor",
     "github>cucumber/renovate-config:gemspec",
-    "github>cucumber/renovate-config:disable-perl"
+    "github>cucumber/renovate-config:disable-perl",
+    "github>cucumber/renovate-config:cpp-deps.txt"
   ],
   "prHourlyLimit": 0
 }