### Is there an existing issue for this?

- [x] I have searched the existing issues

### Current Behavior

Using the local lambda executor, the field `event["requestContex"]["requestTime"]` (code [here](https://github.com/localstack/localstack/blob/52cf2106097c4a46aa9c87095b8682d68c22ed93/localstack/services/apigateway/apigateway_listener.py#L941)) is being passed as a datetime object.  This is breaking lambda code that tries to log the event as in json format.

### Expected Behavior

The AWS behavior (documented [here](https://docs.aws.amazon.com/apigateway/latest/developerguide/http-api-develop-integrations-lambda.html)) is for requestTime to be a string in the format `"04/Mar/2020:19:15:17 +0000"`.

### How are you starting LocalStack?

With a `docker run` command

### Steps To Reproduce

#### How are you starting localstack (e.g., `bin/localstack` command, arguments, or `docker-compose.yml`)

    docker run -it -e TEST_AWS_ACCOUNT_ID="000000000000" -e LOCALSTACK_HOSTNAME="localhost" -e LAMBDA_EXECUTOR="local" -e DEFAULT_REGION="us-west-1" --rm --name localstack_main -p 4566:4566 -p 4571:4571 -p 4590-4593:4590-4593 -p 12121:12121 -p 8080-8081:8080-8081  -v "$(pwd)/localstack:$(pwd)/localstack" -e DOCKER_HOST="unix:///var/run/docker.sock" -e HOST_TMP_FOLDER="$(pwd)/localstack" "localstack/localstack"

#### Client commands (e.g., AWS SDK code snippet, or sequence of "awslocal" commands)

my full environment right now is a bit complex; I could try to make a minimal replication, but I hope this info is enough for now?


### Environment

```markdown
- OS: Ubuntu 18.04
- LocalStack: localstack==0.12.20
```


### Anything else?

Log output
```
2021-11-10T00:25:07:INFO:localstack.services.awslambda.lambda_executors: Error executing Lambda "arn:aws:lambda:us-west-1:000000000000:function:incoming": Object of type datetime is not JSON serializable   File "/opt/code/localstack/localstack/services/awslambda/lambda_executors.py", line 1232, in _execute
    process.run()
  File "/usr/lib/python3.7/multiprocessing/process.py", line 99, in run
    self._target(*self._args, **self._kwargs)
  File "/opt/code/localstack/localstack/services/awslambda/lambda_executors.py", line 1219, in do_execute
    result = lambda_function_callable(inv_context.event, context)
  File "/tmp/localstack/lambda_script_l_cdec33c8.py", line 565, in lambda_handler
    LOGGER.info(f"Incoming event: {json.dumps(event)}")
  File "/usr/lib/python3.7/json/__init__.py", line 231, in dumps
    return _default_encoder.encode(obj)
  File "/usr/lib/python3.7/json/encoder.py", line 199, in encode
    chunks = self.iterencode(o, _one_shot=True)
  File "/usr/lib/python3.7/json/encoder.py", line 257, in iterencode
    return _iterencode(o, 0)
  File "/usr/lib/python3.7/json/encoder.py", line 179, in default
    raise TypeError(f'Object of type {o.__class__.__name__} '

2021-11-10T00:25:07:INFO:localstack.services.awslambda.lambda_api: Error executing Lambda function arn:aws:lambda:us-west-1:000000000000:function:incoming: Object of type datetime is not JSON serializable Traceback (most recent call last):
  File "/opt/code/localstack/localstack/services/awslambda/lambda_api.py", line 813, in run_lambda
    lock_discriminator=lock_discriminator,
  File "/opt/code/localstack/localstack/services/awslambda/lambda_executors.py", line 429, in execute
    return do_execute()
  File "/opt/code/localstack/localstack/services/awslambda/lambda_executors.py", line 419, in do_execute
    return _run(func_arn=func_arn)
  File "/opt/code/localstack/localstack/utils/cloudwatch/cloudwatch_util.py", line 158, in wrapped
    raise e
  File "/opt/code/localstack/localstack/utils/cloudwatch/cloudwatch_util.py", line 154, in wrapped
    result = func(*args, **kwargs)
  File "/opt/code/localstack/localstack/services/awslambda/lambda_executors.py", line 406, in _run
    raise e
  File "/opt/code/localstack/localstack/services/awslambda/lambda_executors.py", line 402, in _run
    result = self._execute(lambda_function, inv_context)
  File "/opt/code/localstack/localstack/services/awslambda/lambda_executors.py", line 1268, in _execute
    raise InvocationException(result, log_output)
localstack.services.awslambda.lambda_executors.InvocationException: Object of type datetime is not JSON serializable
```
import base64
import datetime
import json
import logging
import re
import time
from enum import Enum
from typing import Any, Dict, Optional, Tuple, Union
import requests
from flask import Response as FlaskResponse
from moto.apigateway.models import apigateway_backends
from requests.models import Response
from six.moves.urllib_parse import urljoin
from localstack import config
from localstack.constants import (
    APPLICATION_JSON,
    HEADER_LOCALSTACK_EDGE_URL,