Support custom operationId

[xiaoxiangmoe]

@RestController
public class HelloController {
	@GetMapping(value = "/hello/index")
	public String index() {
		return "Greetings Hello from Spring Boot!";
	}
}

@RestController
public class HiController {
	@GetMapping(value = "/hi/index")
	public String index() {
		return "Greetings Hi from Spring Boot!";
	}
}

In springdoc, it will generate two operations with operationId: index and index_1.

{
  "openapi": "3.0.1",
  "info": { "title": "OpenAPI definition", "version": "v0" },
  "servers": [
    { "url": "http://localhost:8080", "description": "Generated server url" }
  ],
  "tags": [],
  "paths": {
    "/hi/index": {
      "get": {
        "tags": ["hi-controller"],
        "operationId": "index",
        "responses": {
          "200": {
            "description": "OK",
            "content": { "*/*": { "schema": { "type": "string" } } }
          }
        }
      }
    },
    "/hello/index": {
      "get": {
        "tags": ["hello-controller"],
        "operationId": "index_1",
        "responses": {
          "200": {
            "description": "OK",
            "content": { "*/*": { "schema": { "type": "string" } } }
          }
        }
      }
    } 
  },
  "components": {
    "schemas": {}
  }
}

Can we config operationId to controller name + method name?

Such as hiControllerIndex and helloControllerIndex?

[xiaoxiangmoe]

see #675 (comment)