fix(dependabot): Adopt dependabot configs from rust-vmm-ci

linux-loader has not been getting rust-vmm-ci submodule updates since
almost the beginning of the year, as dependabot thinks it exceeded its
open PR limit (this is a bug with open-pull-request-limit: 1 that we
already ran into in the kvm repository a few months ago). Fix this by
adopting the example dependabot configs from rust-vmm-ci, which do not
set open-pull-request-limit.

Signed-off-by: Patrick Roy <[email protected]>

Author: roypat

.github/dependabot.yml

@@ -1,13 +1,29 @@
 version: 2
 updates:
+
+# We do not set open-pull-requests-limit, as sometimes
+# dependabot thinks the limit is hit without actually having
+# any PRs open. In reality, the configs below can only result
+# in at most one PR per package ecosyste manyway.
+# A weekly update of the rust-vmm-ci submodule
 - package-ecosystem: gitsubmodule
   directory: "/"
   schedule:
     interval: weekly
-  open-pull-requests-limit: 1
+    day: monday
+
+# A weekly update to rust dependencies. These will be grouped,
+# e.g. one PR will contains updates for all dependencies.
 - package-ecosystem: cargo
   directory: "/"
-  schedule: 
+  schedule:
     interval: weekly
-  open-pull-requests-limit: 10
-  rebase-strategy: "disabled"
+    day: monday
+  # Make it also update transitive dependencies in Cargo.lock
+  allow:
+    - dependency-type: "all"
+  # Group all available updates into a group called "rust-dependencies"
+  groups:
+    rust-dependencies:
+      patterns:
+        - "*"