Support hidden commands

- CommandRegistration now has a structure to define
  it beind hidden
- Modify relevant parts to filter out hidden commands
- Essentially command is hidden from all other than
  command execution
- Sample in e2e tests
- Fixes #416

spring-shell-samples/src/main/java/org/springframework/shell/samples/e2e/HiddenCommands.java

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2022 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.shell.samples.e2e;
+
+import org.springframework.context.annotation.Bean;
+import org.springframework.shell.command.CommandRegistration;
+import org.springframework.shell.standard.ShellComponent;
+
+@ShellComponent
+public class HiddenCommands extends BaseE2ECommands {
+
+	@Bean
+	public CommandRegistration testHidden1Registration() {
+		return CommandRegistration.builder()
+			.command(REG, "hidden-1")
+			.group(GROUP)
+			.hidden()
+			.withTarget()
+				.function(ctx -> {
+					return "Hello from hidden command";
+				})
+				.and()
+			.build();
+	}
+}