[FEATURE] [SPRING] Add support for custom beanValidation annotations

Description

The feature is mostly inspired by https://bartko-mat.medium.com/openapi-generator-to-spring-boot-with-custom-java-validations-623381df9215

We want to be able to add our custom validation constraint annotations for java spring-based modules.
Provide new vendor extension aka 'x-spring-constraint' and allow user-defined annotation class or package to be imported gracefully using configuration parameters (without any template customization).

This is extremely useful in combination with javax.validation.valueextraction.ValueExctractor , see https://javaee.github.io/javaee-spec/javadocs/javax/validation/valueextraction/package-summary.html

openapi-generator version

6.2.1 , current master

OpenAPI declaration file content or url

openapi: 3.0.3
info:
  version: 1.0.0
  description: Specification to show applicability of x-spring-constraint vendor extension
  title: XSpringConstraintTest Api
paths:
  /smth/add:
    get:
      parameters:
        - in: query
          name: quantity
          schema:
            type: integer
          x-spring-constraint: "@Positive"
          required: true
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                type: boolean
  /smth/remove:
    get:
      parameters:
        - in: query
          name: quantity
          schema:
            type: integer
          x-spring-constraint: "@NotZero(message = \"custom\")"
      responses:
        '200':
          description: OK
          content:
            application/json:
              schema:
                type: boolean

Plugin configuration:

generatorName = 'spring'
configOptions = [
    dateLibrary: 'java8',
    interfaceOnly: 'true',
    openApiNullable: 'false',
    java8: 'false',
    customValidationAnnotationsPackage: 'org.custom.validation.annotations.*'
]

as alternative we can set this property to contains class name to be imported:
customValidationAnnotationsPackage: 'org.custom.validation.annotations.NotZero'

Generates:

package xyz.controller;

import io.swagger.v3.oas.annotations.Operation;
import io.swagger.v3.oas.annotations.Parameter;
import io.swagger.v3.oas.annotations.Parameters;
import io.swagger.v3.oas.annotations.media.Content;
import io.swagger.v3.oas.annotations.media.Schema;
import io.swagger.v3.oas.annotations.responses.ApiResponse;
import io.swagger.v3.oas.annotations.security.SecurityRequirement;
import io.swagger.v3.oas.annotations.tags.Tag;
import org.springframework.http.HttpStatus;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;
import org.springframework.validation.annotation.Validated;
import org.springframework.web.bind.annotation.*;
import org.springframework.web.context.request.NativeWebRequest;
import org.springframework.web.multipart.MultipartFile;
import javax.validation.Valid;
import javax.validation.constraints.*;
import java.util.List;
import java.util.Map;
import java.util.Optional;
import javax.annotation.Generated;
import org.custom.validations.*;

@Generated(value = "org.openapitools.codegen.languages.SpringCodegen", date = "2022-11-07T14:52:46.573574+03:00[Europe/Moscow]")
@Validated
@Tag(name = "smth", description = "the smth API")
public interface SmthApi {

    default Optional<NativeWebRequest> getRequest() {
        return Optional.empty();
    }

    /**
     * GET /smth/add
     *
     * @param quantity  (required)
     * @return OK (status code 200)
     */
    @Operation(operationId = "smthAddGet", responses = { @ApiResponse(responseCode = "200", description = "OK", content = { @Content(mediaType = "application/json", schema = @Schema(implementation = Boolean.class)) }) })
    @RequestMapping(method = RequestMethod.GET, value = "/smth/add", produces = { "application/json" })
    default ResponseEntity<Boolean> smthAddGet(@NotNull @Positive @Parameter(name = "quantity", description = "", required = true) @Valid @RequestParam(value = "quantity", required = true) Integer quantity) {
        return new ResponseEntity<>(HttpStatus.NOT_IMPLEMENTED);
    }

    /**
     * GET /smth/remove
     *
     * @param quantity  (optional)
     * @return OK (status code 200)
     */
    @Operation(operationId = "smthRemoveGet", responses = { @ApiResponse(responseCode = "200", description = "OK", content = { @Content(mediaType = "application/json", schema = @Schema(implementation = Boolean.class)) }) })
    @RequestMapping(method = RequestMethod.GET, value = "/smth/remove", produces = { "application/json" })
    default ResponseEntity<Boolean> smthRemoveGet(@NotZero(message = "custom") @Parameter(name = "quantity", description = "") @Valid @RequestParam(value = "quantity", required = false) Integer quantity) {
        return new ResponseEntity<>(HttpStatus.NOT_IMPLEMENTED);
    }
}

Added with proposed feature:

//lines omitted
import org.custom.validations.*;

//lines omitted
    default ResponseEntity<Boolean> smthAddGet(@NotNull @Positive/* other content omitted*/  Integer quantity) {
        return new ResponseEntity<>(HttpStatus.NOT_IMPLEMENTED);
    }
//lines omitted
    default ResponseEntity<Boolean> smthRemoveGet(@NotZero(message = "custom") /* other content omitted*/ Integer quantity) {
        return new ResponseEntity<>(HttpStatus.NOT_IMPLEMENTED);
    }
}

Command line used for generation

Steps to reproduce

Related issues/PRs

Suggest a fix/enhancement

will propose a solution as PR from fork repository https://github.com/Mintas/openapi-generator

Start from the Spring generator configuration, the x-spring-constraint vendor extension in the supplied OpenAPI example, and the generated Java interface shown in the issue. Verify that custom annotations and the configured package or class imports appear without template customization, and confirm both example parameters generate the requested annotations.