Add Maven and Java codegen npm ecosystems to dependabot.yaml

- Add maven ecosystem entry for /java directory
- Add npm ecosystem entry for /java/scripts/codegen (codegen deps)
- Both use multi-ecosystem-group 'all' matching existing entries

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: edburns

.github/dependabot.yaml

@@ -36,3 +36,13 @@ updates:
     directory: '/dotnet'
     multi-ecosystem-group: 'all'
     patterns: ['*']
+  # Java dependencies
+  - package-ecosystem: 'maven'
+    directory: '/java'
+    multi-ecosystem-group: 'all'
+    patterns: ['*']
+  # Java codegen dependencies
+  - package-ecosystem: 'npm'
+    directory: '/java/scripts/codegen'
+    multi-ecosystem-group: 'all'
+    patterns: ['*']