Update Gradle Dokka configuration to make sure "source" button is visible in all API docs (#516)

Author: whyoleg

.gitignore

@@ -8,3 +8,6 @@ out/
 # Gradle files
 build/
 .gradle/
+
+# generated dokka documentation
+/docs/gradle-plugin/dokka/

kover-gradle-plugin/build.gradle.kts

@@ -2,6 +2,7 @@ import org.jetbrains.kotlin.gradle.dsl.JvmTarget
 import org.jetbrains.kotlin.gradle.dsl.KotlinVersion
 import org.jetbrains.kotlin.gradle.plugin.KotlinCompilation
 import org.jetbrains.kotlin.gradle.tasks.KotlinCompile
+import java.net.*
 
 plugins {
     kotlin("jvm")
@@ -156,6 +157,11 @@ tasks.dokkaHtml {
         perPackageOption {
             skipDeprecated.set(true)
         }
+        sourceLink {
+            localDirectory.set(rootDir)
+            remoteUrl.set(URL("https://github.com/kotlin/kotlinx-kover/tree/main"))
+            remoteLineSuffix.set("#L")
+        }
     }
 }