ci: configure Dependabot for Cargo and GitHub Actions (#2460)

Configures Dependabot to keep Rust / Cargo dependencies and GitHub
Actions workflows up to date.

- Schedules daily dependency checks at 06:00 America/New_York
- Groups Cargo updates into a single consolidated PR with `chore(deps)`
prefix
- Groups GitHub Actions updates into a single consolidated PR with
`ci(deps)` prefix

.github/dependabot.yml

@@ -1,11 +1,30 @@
-# To get started with Dependabot version updates, you'll need to specify which
-# package ecosystems to update and where the package manifests are located.
-# Please see the documentation for all configuration options:
-# https://docs.github.com/github/administering-a-repository/configuration-options-for-dependency-updates
-
 version: 2
 updates:
-  - package-ecosystem: "cargo" # See documentation for possible values
-    directory: "/" # Location of package manifests
+  # Maintain Rust / Cargo dependencies
+  - package-ecosystem: "cargo"
+    directory: "/"
     schedule:
-      interval: "weekly"
+      interval: "daily"
+      time: "06:00"
+      timezone: "America/New_York"
+    # Consolidate updates into a single PR rather than one PR per crate
+    groups:
+      cargo-dependencies:
+        patterns:
+          - "*"
+    commit-message:
+      prefix: "chore(deps)"
+
+  # Maintain GitHub Actions workflows
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "daily"
+      time: "06:00"
+      timezone: "America/New_York"
+    groups:
+      actions:
+        patterns:
+          - "*"
+    commit-message:
+      prefix: "ci(deps)"