Use PoetUtils to set javadoc

PoetUtils.addJavadoc takes care of escaping any '$' characters present in the
javadoc which would otherwise be interpreted as a placeholder by Poet.

Author: dagnir

codegen/src/main/java/software/amazon/awssdk/codegen/poet/client/AsyncClientInterface.java

@@ -71,12 +71,13 @@ public TypeSpec poetSpec() {
         TypeSpec.Builder result = PoetUtils.createInterfaceBuilder(className);
 
         result.addSuperinterface(SdkClient.class)
-              .addJavadoc(getJavadoc())
               .addField(FieldSpec.builder(String.class, "SERVICE_NAME")
                                  .addModifiers(Modifier.PUBLIC, Modifier.STATIC, Modifier.FINAL)
                                  .initializer("$S", model.getMetadata().getSigningName())
                                  .build());
 
+        PoetUtils.addJavadoc(result::addJavadoc, getJavadoc());
+
         if (!model.getCustomizationConfig().isExcludeClientCreateMethod()) {
             result.addMethod(create());
         }

codegen/src/main/java/software/amazon/awssdk/codegen/poet/client/SyncClientInterface.java

@@ -70,12 +70,13 @@ public TypeSpec poetSpec() {
         TypeSpec.Builder result = PoetUtils.createInterfaceBuilder(className);
 
         result.addSuperinterface(SdkClient.class)
-              .addJavadoc(getJavadoc())
               .addField(FieldSpec.builder(String.class, "SERVICE_NAME")
                                  .addModifiers(Modifier.PUBLIC, Modifier.STATIC, Modifier.FINAL)
                                  .initializer("$S", model.getMetadata().getSigningName())
                                  .build());
 
+        PoetUtils.addJavadoc(result::addJavadoc, getJavadoc());
+
         if (!model.getCustomizationConfig().isExcludeClientCreateMethod()) {
             result.addMethod(create());
         }