feat: custom 401/403 error handling for unauthenticated requests

Replace default Spring Security 403 responses with custom 401 (not logged in)
and 403 (insufficient permissions) JSON error responses via exception handling
and global exception handler. Also bump API version to 1.4.0 and add Swagger
annotations for the GitHub webhook controller.

build.gradle.kts

@@ -65,6 +65,7 @@ dependencies {
 
 tasks.processResources {
     filesMatching("application.yaml") {
+        println("appVersion = ${artefactVersion}, channel = ${buildChannel}, vendor = ${vendor}")
         expand(
             "appVersion" to artefactVersion,
             "channel" to buildChannel,