refactor(http): refactoring on http server

[neverchanje]

We have implemented many HTTP APIs so far, some of the codes repeat each time a new API is added.

• argument validation. For example, /meta/app?name=<app_name> requires "name" to be provided, if not, it replies with "bad_request". This case is general. We can eliminate the following codes by filtering illegal requests in http_service::call before the handler.

void meta_http_service::get_app_handler(const http_request &req, http_response &resp)
{
    std::string app_name;
    bool detailed = false;
    for (const auto &p : req.query_args) {
        if (p.first == "name") {
            app_name = p.second;
        } else if (p.first == "detail") {
            detailed = true;
        } else {
            resp.status_code = http_status_code::bad_request;
            return;
        }
    }

• Thrift-struct conversion to human-readable JSON. Currently table_printer is the general-used utility for this purpose. However table_printer is designed to support both "table" and "JSON" format, for JSON format, we should use a dedicated JSON library, like rapidjson, and nlohmann/json.

• redirect_if_not_primary. We add primary-meta-check in every handler. We can eliminate them by prepending this call before meta_http_service::call.

void meta_http_service::get_app_envs_handler(const http_request &req, http_response &resp)
{
    if (!redirect_if_not_primary(req, resp))
        return;