Add cast to environment variables

[sylvainmouquet]

#2730
#4347

Currently, the environment variables are string only.
This patch try to cast a variable to his natural type.
It's possible to get a string every time with using this format : ${FOO:-"1"}

Unit tests

 assert defaults_interpolator("${BAR:-1}") == 1
assert defaults_interpolator("${BAR:--1}") == -1
assert defaults_interpolator("${BAR:-1.2}") == 1.2
assert defaults_interpolator("${BAR:-True}") == True
assert defaults_interpolator("${BAR:-False}") == False
assert defaults_interpolator("${BAR:-\"True\"}") == "True"
assert defaults_interpolator("${BAR:-\"False\"}") == "False"
assert defaults_interpolator("${BAR:-\"1\"}") == "1"
assert defaults_interpolator("${BAR:-\"1.2\"}") == "1.2"
assert defaults_interpolator("${BAR:-\"foo\"}") == "foo"

Sample file sample-compose.yml

version: "3.3"
networks:
default:
external:
name: ${NETWORK_NAME:-"1"}
services:
monservice:
image: alpine
command: nc -lp1789
ports:
- "1789:1789"
deploy:
replicas: ${NC_REPLICAS:-1}

before:

$ docker-compose -f ../../../Desktop/sample-compose.yml config
ERROR: The Compose file '.\../../../Desktop/sample-compose.yml' is invalid because:
services.monservice.deploy.replicas contains an invalid type, it should be an integer

after:

$ docker-compose -f ../../../Desktop/sample-compose.yml config
WARNING: Some services (monservice) use the 'deploy' key, which will be ignored. Compose does not support 'deploy' configuration - use `docker stack deploy` to deploy to a swarm.
networks:
default:
external:
name: '1'
services:
monservice:
command: nc -lp1789
deploy:
replicas: 1
image: alpine
ports:
- published: 1789
target: 1789
version: '3.3'

[shin-]

Closing in favor of #5291

Thank you!