apacheGH-39088: [Dev][Java] Add Dependabot configuration for Java (ap…

…ache#39089)

### Rationale for this change

We can add `MINOR: [Java] ` prefix to PRs from Dependabot automatically.

### What changes are included in this PR?

Add a configuration for Maven.

### Are these changes tested?

No. I want to test this by merging this to main.

### Are there any user-facing changes?

No.
* Closes: apache#39088

Authored-by: Sutou Kouhei <kou@clear-code.com>
Signed-off-by: David Li <li.davidm96@gmail.com>

.github/dependabot.yml

@@ -23,6 +23,12 @@ updates:
       interval: "weekly"
     commit-message:
       prefix: "MINOR: [CI] "
+  - package-ecosystem: "maven"
+    directory: "/java/"
+    schedule:
+      interval: "weekly"
+    commit-message:
+      prefix: "MINOR: [Java] "
   - package-ecosystem: "npm"
     directory: "/js/"
     schedule: