Add configuration for changelog generator

This commits adds a dedicated configuration to be used when invoking
the github changelog generator. This custom configuration makes sure
to sort dependency upgrades based on the issue title.

Closes gh-23484

ci/config/changelog-generator.yml

+changelog:
+  repository: spring-projects/spring-boot
+  sections:
+    - title: ":star: New Features"
+      labels:
+        - "type: enhancement"
+    - title: ":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"

ci/scripts/generate-changelog.sh

 #!/bin/bash
 set -e
 
+CONFIG_DIR=git-repo/ci/config
 version=$( cat version/version )
 
 milestone=${version}
@@ -9,7 +10,7 @@ if [[ $RELEASE_TYPE = "RELEASE" ]]; then
 fi
 
 java -jar /github-changelog-generator.jar \
-  --changelog.repository=spring-projects/spring-boot  \
+  --spring.config.location=${CONFIG_DIR}/changelog-generator.yml \
   ${milestone} generated-changelog/changelog.md
 
 echo ${version} > generated-changelog/version