Support for content in top-level config

[jvitor83]

What would you like to be added?

Support for content in the top-level config as it states in https://docs.docker.com/reference/compose-file/configs/ released in Docker Compose version 2.23.1

services:

  hello:
    image: nginxdemos/hello
    configs:
      - source: conf-name
        target: /etc/dynamic.yaml

configs:
  conf-name:
    content: |
      some-setting: true

Currently it gives:
FATA Unable to retrieve file: Unable to read file: open : The system cannot find the file specified.

Why is this needed?

To keep the compatibility synced between docker-compose and kompose.