[Java][Spring] Add Spring pagination with vendor extension x-spring-paginated

Created by: david1601

PR detail By setting of x-spring-paginated: true for an operation in the yaml file at the same level as operationId this pull request add a Spring Pageable (org.springframework.data.domain.Pageable) parameter if JavaSpring is used.

The idea for the solution based on: https://github.com/swagger-api/swagger-codegen/pull/3357.

Spring Pageable: https://docs.spring.io/spring-data/commons/docs/current/api/org/springframework/data/domain/Pageable.html

In yaml-file: operationId: findPetsByTags x-spring-paginated: true

Created PetApi.java:

    @ApiOperation(value = "Finds Pets by tags", nickname = "findPetsByTags", notes = "Multiple tags can be provided with comma separated strings. Use tag1, tag2, tag3 for testing.", response = Pet.class, responseContainer = "List", authorizations = {
        @Authorization(value = "petstore_auth", scopes = {
            @AuthorizationScope(scope = "write:pets", description = "modify pets in your account"),
            @AuthorizationScope(scope = "read:pets", description = "read your pets")
            })
    }, tags={ "pet", })
    @ApiImplicitParams({
        @ApiImplicitParam(name = "page", dataType = "integer", paramType = "query",
                value = "Results page you want to retrieve (0..N)"),
        @ApiImplicitParam(name = "size", dataType = "integer", paramType = "query",
                value = "Number of records per page."),
        @ApiImplicitParam(name = "sort", allowMultiple = true, dataType = "string", paramType = "query",
                value = "Sorting criteria in the format: property(,asc|desc). " +
                        "Default sort order is ascending. " +
                        "Multiple sort criteria are supported.")
    })
    @ApiResponses(value = { 
        @ApiResponse(code = 200, message = "successful operation", response = Pet.class, responseContainer = "List"),
        @ApiResponse(code = 400, message = "Invalid tag value") })
    @RequestMapping(value = "/pet/findByTags",
        produces = { "application/xml", "application/json" }, 
        method = RequestMethod.GET)
    default ResponseEntity<List<Pet>> findPetsByTags(@NotNull @ApiParam(value = "Tags to filter by", required = true) @Valid @RequestParam(value = "tags", required = true) List<String> tags, @ApiIgnore final Pageable pageable) {

PR checklist

• Read the contribution guidelines.
• If contributing template-only or documentation-only changes which will change sample output, build the project before.
• Run the shell script(s) under ./bin/ (or Windows batch scripts under .\bin\windows) to update Petstore samples related to your fix. This is important, as CI jobs will verify all generator outputs of your HEAD commit, and these must match the expectations made by your contribution. You only need to run ./bin/{LANG}-petstore.sh, ./bin/openapi3/{LANG}-petstore.sh if updating the code or mustache templates for a language ({LANG}) (e.g. php, ruby, python, etc).
• File the PR against the correct branch: master, 4.3.x, 5.0.x. Default: master.
• Copy the technical committee to review the pull request if your PR is targeting a particular programming language.

Technical committee for programming language Java: @bbdouglas (2017/07) @sreeshas (2017/08) @jfiala (2017/08) @lukoyanov (2017/09) @cbornet (2017/09) @jeff9finger (2018/01) @karismann (2019/03) @Zomzog (2019/04) @lwlee2608 (2019/10)