Simplify Dokka configuration with auto-discovery

Replace static `dokkaProjects` list with dynamic Kotlin source
detection, eliminating manual maintenance and improving automation.

- Remove `dokkaProjects` list from ext block that required manual
  updates when adding Kotlin modules
- Move Dokka plugin and configuration back into main `javaProjects`
  configure block for simpler structure
- Update `docsZip` task to dynamically find projects with Kotlin
  sources using `javaProjects.findAll {it.file('src/main/kotlin').
  exists()}` instead of referencing static list
- Change output directory API from `buildDirectory.file('kdoc')` to
  `buildDirectory.dir('kdoc')` for semantically correct directory
  reference

Author: cppwfs

build.gradle

@@ -116,10 +116,6 @@ ext {
 
     javaProjects = subprojects - project(':spring-integration-bom')
 
-    // Modules that have Kotlin sources to document using dokka
-    dokkaProjects = [
-            'spring-integration-core'
-    ]
 }
 
 allprojects {
@@ -412,14 +408,12 @@ configure(javaProjects) { subproject ->
             }
         }
     }
-}
 
-// Process only the modules that require kotlin docs
-configure(subprojects.findAll { dokkaProjects.contains(it.name) }) { subproject ->
+    // Process only the modules that require kotlin docs
     apply plugin: 'org.jetbrains.dokka'
     dokka {
         dokkaPublications.html {
-            outputDirectory.set(file(rootProject.layout.buildDirectory.file('kdoc')))
+            outputDirectory.set(file(rootProject.layout.buildDirectory.dir('kdoc')))
         }
         dokkaSourceSets.configureEach {
             sourceRoots.setFrom(file('src/main/kotlin'))
@@ -1143,7 +1137,7 @@ tasks.register('schemaZip', Zip) {
 }
 
 tasks.register('docsZip', Zip) {
-    dependsOn dokkaProjects.collect { ":${it}:dokkaGenerate" }
+    dependsOn javaProjects.findAll { it.file('src/main/kotlin').exists() }.collect { ":${it.name}:dokkaGenerate" }
     group = 'Distribution'
     archiveClassifier = 'docs'
     description = "Builds -${archiveClassifier} archive containing api and reference " +