Is there a way to feed GCP logging a JSON payload such that it grabs the level and timestamp from the payload?

I am creating a log receiver, which will receive the logging output of another go program, do some filtering and then directly POST to GCP logging. The logging received are pure JSON entries. I'd rather avoid a JSON marshall if I can. Just adding the JSON as JSON payload to the log entry would not pick up the level --> Severity or the timestamp. I can force feed the Severity, but my attempt at the timestamp is failing. Best case, however, would be to have a JSON string and a tiny bit of configuration that says find Severity in level and use the timestamp field. Here is my minimal example:

package main

import (
    "context"
    "encoding/json"
    "fmt"
    "log"
    "time"

    "cloud.google.com/go/logging"
)

func main() {
    ctx := context.Background()
    projectID := "redacted1"
    client, err := logging.NewClient(ctx, projectID)
    if err != nil {
        log.Fatalf("Failed to create client: %v", err)
    }
    logName := "redacted2"
    logger := client.Logger(logName)
    // JSON string
    text := "{\"decision_id\":\"21986d12-e3b2-47f3-b3c7-9a8d77bd048d\",\"input\":{\"networks\":[{\"id\":\"net1\",\"public\":false},{\"id\":\"net2\",\"public\":false},{\"id\":\"net3\",\"public\":true},{\"id\":\"net4\",\"public\":true}],\"ports\":[{\"id\":\"p1\",\"network\":\"net1\"},{\"id\":\"p2\",\"network\":\"net3\"},{\"id\":\"p3\",\"network\":\"net2\"}],\"servers\":[{\"id\":\"app\",\"ports\":[\"p1\",\"p2\",\"p3\"],\"protocols\":[\"https\",\"ssh\"]},{\"id\":\"db\",\"ports\":[\"p3\"],\"protocols\":[\"mysql\"]},{\"id\":\"cache\",\"ports\":[\"p3\"],\"protocols\":[\"memcache\"]},{\"id\":\"ci\",\"ports\":[\"p1\",\"p2\"],\"protocols\":[\"http\"]},{\"id\":\"busybox\",\"ports\":[\"p1\"],\"protocols\":[\"telnet\"]}]},\"labels\":{\"id\":\"d29ba0a9-75d4-4d74-9d03-7bf0399a47c3\",\"version\":\"0.23.2\"},\"level\":\"info\",\"metrics\":{\"counter_server_query_cache_hit\":0,\"timer_rego_input_parse_ns\":554348,\"timer_rego_query_compile_ns\":484825,\"timer_rego_query_eval_ns\":1002441,\"timer_rego_query_parse_ns\":46624,\"timer_server_handler_ns\":2290410},\"msg\":\"Decision Log\",\"path\":\"example/violation\",\"requested_by\":\"127.0.0.1:44934\",\"result\":[\"ci\",\"busybox\"],\"time\":\"2021-01-04T08:44:24-06:00\",\"timestamp\":\"2021-01-04T14:44:24.215618442Z\",\"type\":\"openpolicyagent.org/decision_logs\"}"
    sev := logging.Info
    tim, err := time.Parse(time.RFC3339Nano, "2021-01-04T14:44:24.215618442Z")
    if err != nil {
        log.Fatalf("Failed to parse time: %v", err)
    }
    entry := logging.Entry{Payload: json.RawMessage([]byte(text)), Severity: sev,
        Timestamp: tim}
    err = logger.LogSync(ctx, entry)
    if err != nil {
        log.Fatalf("Failed to flush client: %v", err)
    }
    err = client.Close()
    if err != nil {
        log.Fatalf("Failed to close client: %v", err)
    }
}