Add workflow to release on Maven Central

This commit adds a standard GHA workflow to perform a release, including
syncing with Maven Central using s01.oss.sonatype.org.

The release workflow kicks off based on tag that matches `vX.Y.Z` and
perform the following:

* Build the project
* Stage the bits to repo.spring.io
* Move the staging bits to Maven Central
* Promote the bits to repo.spring.io/release
* Generate a changelog using the issues matching the version

Closes gh-1812

.github/actions/create-github-release/changelog-generator.yml

@@ -0,0 +1,23 @@
+changelog:
+  repository: spring-projects/spring-webflow
+  sections:
+    - title: ":star: New Features"
+      labels:
+        - "type: enhancement"
+    - title: ":lady_beetle: Bug Fixes"
+      labels:
+        - "type: bug"
+        - "type: regression"
+    - title: ":notebook_with_decorative_cover: Documentation"
+      labels:
+        - "type: documentation"
+    - title: ":hammer: Dependency Upgrades"
+      sort: "title"
+      labels:
+        - "type: dependency-upgrade"
+  contributors:
+    exclude:
+      names:
+        - "bclozel"
+        - "rstoyanchev"
+        - "snicoll"