Add JsonString recipe to examples (#1230)

* Start recipes module with JsonString recipe

* Make recipes a kotlin project

* Move JsonString sample to examples

* Add license

* Include all java modules

* Add kotlin options

* Spotless

* Remove jvmtarget

I was today years old when I found out 1.7 isn't a valid target

* Make gradle happy

* Add codegen

* Spotless

examples/build.gradle.kts

@@ -14,11 +14,21 @@
  * limitations under the License.
  */
 
+import org.jetbrains.kotlin.gradle.tasks.KotlinCompile
+
 plugins {
-  `java-library`
+  kotlin("jvm")
+  kotlin("kapt")
+}
+
+tasks.withType<KotlinCompile>().configureEach {
+  kotlinOptions {
+    freeCompilerArgs = listOf("-progressive")
+  }
 }
 
 dependencies {
+  kapt(project(":kotlin:codegen"))
   compileOnly(Dependencies.jsr305)
   implementation(project(":moshi"))
   implementation(project(":adapters"))