[Python-Flask] Default Dockerfile should pull `python:3.8-alpine`

Description

Python-flask generated code, once put into a docker container could not recognize arrays of strings and reported None until I updated the python container from FROM python:3.6-alpine to FROM Python:3.8-alpine.

Swagger-codegen version

Exported from swaggerhub.com so what ever is there.

Swagger declaration file content or url

https://app.swaggerhub.com/apis/lwileczek-dmc/caml-measurements/1.1.0

Command line used for generation

docker build . -t example_app:1.0.0
docker run --rm -p 8080:8080 -d example_app:1.0.0
curl -X POST 'http://localhost:8080/api/v1/write' -H "Content-Type: application/json" -d '
{
    "measurements":  {
        "performer": "team0", 
        "system": "dell", 
        "experiment": "myfile12.csv", 
        "replication-id": "4", 
        "replication-settings": {
            "rain": "heavy",
            "fog": false
        }, 
        "inference-system-time": "2021-12-31T23:59:60Z", 
        "inference-id": 333, 
        "inference-true-conditions": {
            "fog": true,
            "snow": true,
            "wind": true
        }, 
        "ml-strategy": "tree", 
        "ml-performance": 0.2, 
        "caml-conditions": ["horse", "car"], 
        "caml-performance": 0.6, 
        "caml-strategy": "tree" 
    },
    "connection": {"url": "http://localhost", "port": 9200, "username": "None", "password": "None", "index": "testcaml"} 
}'

The error is thrown by "caml-conditions": ["horse", "car"],

Suggest a fix/enhancement

generated dockerfile should pull from python:3.8-alpine.

Locate the Python-Flask generated Dockerfile template and inspect the base-image line; the issue identifies the current and desired Python Alpine images. Update the default to python:3.8-alpine, then run the provided docker build and docker run commands to verify the generated container uses the requested image and handles the example request.