Add Dependabot

These are excluded:
* org.jruby:jruby, depends on AsciidoctorJ
* org.apache.maven:*, pinned Maven version
* org.apache.maven.plugin-tools:*, pinned Maven version
* org.apache.maven.doxia:*, pinned Maven Doxia version
* org.codehaus.plexus:*, pinned Maven version
* commons-io:commons-io, depends on Maven runtime

.github/dependabot.yml

@@ -0,0 +1,40 @@
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+    labels:
+      - "dependencies"
+  - package-ecosystem: "maven"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+    labels:
+      - "dependencies"
+    commit-message:
+      prefix: "(main)"
+    target-branch: "main"
+    ignore:
+      - dependency-name: org.jruby:jruby
+      - dependency-name: org.apache.maven:*
+      - dependency-name: org.apache.maven.plugin-tools:*
+      - dependency-name: org.apache.maven.doxia:*
+      - dependency-name: org.codehaus.plexus:*
+      - dependency-name: commons-io:commons-io
+  - package-ecosystem: "maven"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+    labels:
+      - "dependencies"
+    commit-message:
+      prefix: "(v2.2.x)"
+    target-branch: "v2.2.x"
+    ignore:
+      - dependency-name: org.jruby:jruby
+      - dependency-name: org.apache.maven:*
+      - dependency-name: org.apache.maven.plugin-tools:*
+      - dependency-name: org.apache.maven.doxia:*
+      - dependency-name: org.codehaus.plexus:*
+      - dependency-name: commons-io:commons-io

CHANGELOG.adoc

@@ -37,6 +37,7 @@ Build / Infrastructure::
   * Use Maven v3.9.2 in CI and wrapper (#658)
   * Use Maven v3.9.5 in CI and wrapper (#662)
   * Add Java 21 to CI (#664)
+  * Add Dependabot to automate dependency management (#669)
 
 Documentation::