MNT: add Renovate config to master so it actually takes effect (#1039)

Renovate (Mend hosted app) reads repository configuration only from the
default branch, which is `master`. The config introduced in #972 was merged
into `develop`, so it never took effect: Renovate ran with bare defaults,
raised PRs against `master` instead of `develop`, did not group updates, and
naively bumped every pinned line in the autogenerated `docs/requirements.txt`.

This adds the configuration on `master` and:
- keeps the intended settings (baseBranches: develop, grouping, labels,
  dependency dashboard);
- enables the `pip-compile` manager scoped to `docs/requirements.txt`, which is
  autogenerated from `docs/requirements.in`, so the lock file is regenerated
  properly instead of patched line by line;
- disables the `pip_requirements` manager for that one file to avoid duplicate
  PRs (it still manages the hand-written requirements files).

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: Gui-FernandesBR

.github/renovate.json

@@ -0,0 +1,42 @@
+{
+  "$schema": "https://docs.renovatebot.com/renovate-schema.json",
+  "extends": [
+    "config:recommended"
+  ],
+  "baseBranches": [
+    "develop"
+  ],
+  "labels": [
+    "dependencies"
+  ],
+  "dependencyDashboard": true,
+  "automerge": false,
+  "pip-compile": {
+    "managerFilePatterns": [
+      "/^docs/requirements\\.txt$/"
+    ]
+  },
+  "packageRules": [
+    {
+      "matchPackagePatterns": [
+        "*"
+      ],
+      "matchUpdateTypes": [
+        "minor",
+        "patch"
+      ],
+      "groupName": "all non-major dependencies",
+      "groupSlug": "all-non-major"
+    },
+    {
+      "description": "docs/requirements.txt is autogenerated by pip-compile from docs/requirements.in. Let the pip-compile manager regenerate the lock file, and stop the pip_requirements manager from editing the autogenerated file line by line.",
+      "matchManagers": [
+        "pip_requirements"
+      ],
+      "matchFileNames": [
+        "docs/requirements.txt"
+      ],
+      "enabled": false
+    }
+  ]
+}