chore: Group upper bound dependencies file deps (#3941)

Tested in lqiu96#22

These rules need to be added to the end as renovate `packageRules`
configurations are `mergeable`. This means that it scans the rules
top-down and each subsequent matching rules gets its configurations
overwritten. This tries to make it so that only the `dependencies.txt`
are in its own file.

Author: lqiu96

renovate.json

@@ -12,7 +12,7 @@
   "customManagers": [
     {
       "customType": "regex",
-      "managerFilePatterns": ["/^dependencies\\.txt$/"],
+      "fileMatch": ["dependencies.txt"],
       "matchStrings": ["(?<depName>.*),(.*)=(?<currentValue>.*)"],
       "datasourceTemplate": "maven"
     },
@@ -216,6 +216,15 @@
       "matchPackageNames": [
         "/^com.google.errorprone/"
       ]
+    },
+    {
+      "matchManagers": [
+        "regex"
+      ],
+      "matchFileNames": ["dependencies.txt"],
+      "matchDatasources": ["maven"],
+      "groupName": "Upper Bound Dependencies File",
+      "description": "Group all dependencies from the Upper Bound Dependencies File"
     }
   ]
 }