Improve repository.

- add kokuwa checkstyle
- add dependabot
- add dependency documentation
- add code owners
- add codeql
- add license badge

.github/dependabot.yml

@@ -0,0 +1,15 @@
+version: 2
+updates:
+  - package-ecosystem: maven
+    directory: /
+    schedule:
+      interval: daily
+    open-pull-requests-limit: 1
+    rebase-strategy: auto
+    ignore:
+      - dependency-name: ch.qos.logback:logback-classic
+        update-types: ["version-update:semver-major", "version-update:semver-minor"]
+  - package-ecosystem: github-actions
+    directory: /
+    schedule:
+      interval: daily