Publish to Gradle Central Plugin Repository

Update CI to set the attributes required for publishing to the
Gradle Central Plugin Repository.

Closes gh-150

ci/scripts/promote.sh

@@ -61,6 +61,14 @@ if [[ ${RELEASE_TYPE} = "RELEASE" ]]; then
 	if [[ $artifactsPublished = "false" ]]; then
 		echo "Failed to publish"
 		exit 1
+	else
+		curl \
+			-s \
+			-u ${BINTRAY_USERNAME}:${BINTRAY_API_KEY} \
+			-H "Content-Type: application/json" \
+			-d '[ { "name": "gradle-plugin", "values": ["io.spring.javaformat:io.spring.javaformat:spring-javaformat-gradle-plugin"] } ]' \
+			-X POST \
+			https://api.bintray.com/packages/${BINTRAY_SUBJECT}/${BINTRAY_REPO}/${groupId}/versions/${version}/attributes  > /dev/null || { echo "Failed to add attributes" >&2; exit 1; }
 	fi
 fi