New publication configuration (#14)

* add Dokka + align POM metadatas with sonatype requirements

* update snapshot CI

* update JNI publication

* update CI scripts

* remove maven-metadata-local.xml

* add snapshot publication with maven-publish plugin

jni/jvm/all/build.gradle.kts

@@ -1,5 +1,6 @@
 plugins {
     `java-library`
+    id("org.jetbrains.dokka")
     `maven-publish`
 }
 
@@ -14,6 +15,10 @@ publishing {
         create<MavenPublication>("jvm") {
             artifactId = "secp256k1-kmp-jni-jvm"
             from(components["java"])
+            val sourcesJar = task<Jar>("sourcesJar") {
+                archiveClassifier.set("sources")
+            }
+            artifact(sourcesJar)
         }
     }
 }