create PublishingConfig and configurePublishing function

buildSrc/src/main/kotlin/com/dfsek/terra/PublishingConfig.kt

@@ -0,0 +1,33 @@
+package com.dfsek.terra
+
+import org.gradle.api.Project
+import org.gradle.api.publish.PublishingExtension
+import org.gradle.api.publish.maven.MavenPublication
+import org.gradle.kotlin.dsl.*
+
+fun Project.configurePublishing() {
+    configure<PublishingExtension> {
+        publications {
+            create<MavenPublication>("mavenJava") {
+                artifact(tasks["sourcesJar"])
+                artifact(tasks["jar"])
+            }
+        }
+
+        repositories {
+            val mavenUrl = "https://repo.codemc.io/repository/maven-releases/"
+            //val mavenSnapshotUrl = "https://repo.codemc.io/repository/maven-snapshots/"
+
+            maven(mavenUrl) {
+                val mavenUsername: String? by project
+                val mavenPassword: String? by project
+                if (mavenUsername != null && mavenPassword != null) {
+                    credentials {
+                        username = mavenUsername
+                        password = mavenPassword
+                    }
+                }
+            }
+        }
+    }
+}