add OpenAPI 3 docs for REST endpoints (#910)

remarks:
- the format is JSON
- it is a "live" and dynamic documentation reflecting the runtime.
- it can be retrieved at /manager/v3/api-docs of a running steve instance
- only enabled for PROD profile

src/main/java/de/rwth/idsg/steve/config/ApiDocsConfiguration.java

@@ -0,0 +1,68 @@
+/*
+ * SteVe - SteckdosenVerwaltung - https://github.com/steve-community/steve
+ * Copyright (C) 2013-2019 RWTH Aachen University - Information Systems - Intelligent Distributed Systems Group (IDSG).
+ * All Rights Reserved.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+package de.rwth.idsg.steve.config;
+
+import de.rwth.idsg.steve.SteveConfiguration;
+import de.rwth.idsg.steve.SteveProdCondition;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Conditional;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.web.bind.annotation.RestController;
+import springfox.documentation.builders.ApiInfoBuilder;
+import springfox.documentation.oas.annotations.EnableOpenApi;
+import springfox.documentation.spi.DocumentationType;
+import springfox.documentation.spring.web.plugins.Docket;
+
+import static springfox.documentation.builders.RequestHandlerSelectors.withClassAnnotation;
+
+/**
+ * @author Sevket Goekay <sevketgokay@gmail.com>
+ * @since 15.09.2022
+ */
+@Configuration
+@EnableOpenApi
+@Conditional(SteveProdCondition.class)
+public class ApiDocsConfiguration {
+
+    static {
+        // Set the path with prefix /manager to protect the documentation behind regular sign-in
+        // Default is just /v3/api-docs
+        System.setProperty("springfox.documentation.open-api.v3.path", "/manager/v3/api-docs");
+    }
+
+    @Bean
+    public Docket apiDocs() {
+        String title = "SteVe REST API Documentation";
+
+        var apiInfo = new ApiInfoBuilder()
+            .title(title)
+            .description(title)
+            .license("GPL-3.0")
+            .licenseUrl("https://github.com/steve-community/steve/blob/master/LICENSE.txt")
+            .version(SteveConfiguration.CONFIG.getSteveVersion())
+            .build();
+
+        return new Docket(DocumentationType.OAS_30)
+            .useDefaultResponseMessages(false)
+            .apiInfo(apiInfo)
+            .select()
+            .apis(withClassAnnotation(RestController.class))
+            .build();
+    }
+}