fix: mixing runtimes and architectures

while running a setup where combining Python and NodeJS lambda's, I ran into a couple of issues:

1) packaging of mixed runtime (as mentioned in #688 ) would lead to the following error:

STDOUT:  Error:
[OperationalError: ENOENT: no such file or directory, scandir '.serverless/requirements'] {
  cause: [Error: ENOENT: no such file or directory, scandir '.serverless/requirements'] {
    errno: -2,
    code: 'ENOENT',
    syscall: 'scandir',
    path: '.serverless/requirements'
  },
  isOperational: true,
  errno: -2,
  code: 'ENOENT',
  syscall: 'scandir',
  path: '.serverless/requirements'
}

2) dockerizePip image would always default to provider.runtime / provider.architecture which would lead to the following error:

Running "docker run --rm <mounts> -u 0 public.ecr.aws/sam/build-nodejs18.x:latest-arm64 python -m pip install -t /var/task/ -r /var/task/requirements.txt --cache-dir /var/useDownloadCache" failed with: "/usr/bin/python: No module named pip"

therefore I've adjusted 1) zipping to be to only be performed on either functions which runtimes are specifically python, or no runtime is set and provider.runtime is python3.

2) to take function options as argument for retrieving the docker image.

serverless / serverless-python-requirements

fix: mixing runtimes and architectures #815