Add Maven Timeline plugin and upload artifact in CI

The license-maven-plugin is already bound to process-sources phase in pom.xml,
so mvn verify already runs it. The separate mvn license:check step was
overwriting target/timeline/ with only its own data.

Author: jeanbisutti

.github/workflows/CI.yml

@@ -25,7 +25,11 @@ jobs:
         cache: 'maven'
     - name: Execute tests
       run: mvn verify
-    - name: check license header is present in all files
-      run: mvn license:check
+    - name: Upload Maven Timeline
+      if: always()
+      uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4
+      with:
+        name: maven-timeline-java-${{ matrix.java }}
+        path: target/timeline/
     - name: Upload coverage to Codecov
       uses: codecov/codecov-action@75cd11691c0faa626561e295848008c8a7dddffe # v5

.mvn/extensions.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<extensions>
+  <extension>
+    <groupId>io.takari.maven</groupId>
+    <artifactId>maven-timeline</artifactId>
+    <version>2.0.4</version>
+  </extension>
+</extensions>