Default boolean arg to false

- In a case where arg is given as boolean and with plain
  @ShellOption (user doesn't define defaults), configure
  arg not to be mandatory and with default value false.
- This brings this spesific case more close how it behave
  in older shell version.
- Having `@ShellOption boolean arg1` it now works as:
    my-shell:>e2e reg default-value-boolean3
    Hello false
    my-shell:>e2e reg default-value-boolean3 --arg1
    Hello true
    my-shell:>e2e reg default-value-boolean3 --arg1 false
    Hello false
    my-shell:>e2e reg default-value-boolean3 --arg1 true
    Hello true
- Fixes #461

spring-shell-standard/src/main/java/org/springframework/shell/standard/StandardMethodTargetRegistrar.java

@@ -158,7 +158,13 @@ public class StandardMethodTargetRegistrar implements MethodTargetRegistrar, App
 								optionSpec.defaultValue(so.defaultValue());
 							}
 							if (ObjectUtils.nullSafeEquals(so.defaultValue(), ShellOption.NONE)) {
-								optionSpec.required();
+								if (ClassUtils.isAssignable(boolean.class, parameterType)) {
+									optionSpec.required(false);
+									optionSpec.defaultValue("false");
+								}
+								else {
+									optionSpec.required();
+								}
 							}
 							if (!ClassUtils.isAssignable(NoValueProvider.class, so.valueProvider())) {
 								CompletionResolver completionResolver = ctx -> {