Initialize new request files from cli

[kyleect]

reqlang create examples/valid/new.reqlang \
    --vars value \
    --envs local, prod \
    --set local value=123 \
    --set prod value=456 \
    --verb POST \
    --target 'https://example.com?env={{@env}}' \
    --header content-type=application/json \
    --body '[1, 2, 3]'

Acceptance Criteria

• Declare variables using --vars
  • Error on duplicates
• Declare environments using --envs name1, name2
  • Error on duplicates
  • Error trying to pass default
• Set environment specific values for variables using --set env_name key=value
  • Error on environment names not defined
• Set all details of the request
  • --verb
  • --target
  • --header key=value
  • --body value
  • --http version defaults to 1.1
• Response is out of scope