Add build artifact containing json file of all wire compatible versions (elastic#123740) (elastic#124038)

(cherry picked from commit e54037b)

# Conflicts:
#	build.gradle

Author: mark-vieira

build.gradle

@@ -218,6 +218,22 @@ tasks.register("verifyVersions") {
   }
 }
 
+def generateUpgradeCompatibilityFile = tasks.register("generateUpgradeCompatibilityFile") {
+  def outputFile = project.layout.buildDirectory.file("rolling-upgrade-compatible-${VersionProperties.elasticsearch}.json")
+  def rollingUpgradeCompatibleVersions = buildParams.bwcVersions.wireCompatible - VersionProperties.elasticsearchVersion
+  inputs.property("rollingUpgradeCompatibleVersions", rollingUpgradeCompatibleVersions)
+  outputs.file(outputFile)
+  doLast {
+    def versionsString = rollingUpgradeCompatibleVersions.collect { "\"${it.toString()}\"" }.join(', ')
+    outputFile.get().asFile.write("""{"rolling_upgrade_compatible_versions" : [${versionsString}]}""")
+  }
+}
+
+def upgradeCompatibilityZip = tasks.register("upgradeCompatibilityZip", Zip) {
+  archiveFile.set(project.layout.buildDirectory.file("rolling-upgrade-compatible-${VersionProperties.elasticsearch}.zip"))
+  from(generateUpgradeCompatibilityFile)
+}
+
 /*
  * When adding backcompat behavior that spans major versions, temporarily
  * disabling the backcompat tests is necessary. This flag controls
@@ -486,6 +502,7 @@ tasks.register("buildReleaseArtifacts").configure {
   }
     .collect { GradleUtils.findByName(it.tasks, 'assemble') }
     .findAll { it != null }
+  dependsOn upgradeCompatibilityZip
 }
 
 tasks.register("spotlessApply").configure {