Add KuberenetesWorker.submit for ad-hoc submission to a Kubernetes work pool

[desertaxle]

This PR adds an experimental .submit method to the KubernetesWorker class to allow a flow to be submitted to a Kubernetes cluster. The updates to the work pool API haven't been made yet, so the steps for bundle upload and execution are stored within the work pool's env field on the base job template.

Here's an example:

import asyncio
import json
import os

from prefect_kubernetes import KubernetesWorker

from prefect import flow

# These steps are stored in `env` in the work pool's base job template
UPLOAD_STEP = {
    "prefect_aws.experimental.bundles.upload": {
        "requires": "prefect-aws==0.5.5",
        "bucket": "storage-blocks-test-bucket",
        "aws_credentials_block_name": "my-creds",
    }
}

EXECUTE_STEP = {
    "prefect_aws.experimental.bundles.execute": {
        "requires": "prefect-aws==0.5.5",
        "bucket": "storage-blocks-test-bucket",
        "aws_credentials_block_name": "my-creds",
    }
}


@flow(log_prints=True, result_storage="s3-bucket/results-bucket")
def my_flow():
    print("Returning greeting...")
    return "Hello, world!"


async def main():
    async with KubernetesWorker(work_pool_name="olympic") as worker:
        future = await worker.submit(flow=my_flow)

    print(future.result()) # prints "Hello, world!"


if __name__ == "__main__":
    asyncio.run(main())

Related to #17194

[codspeed-hq]

CodSpeed Performance Report

Merging #17218 will not alter performance

_{Comparing k8s-worker-submit (d18f090) with main (ab2634c)}

Summary

✅ 2 untouched benchmarks

[cicdw]

noticed a few things but overall is looking good