Pass environment variables to `apify push` and toggle `applyEnvVarsToBuild`

[janbuchar]

• The environmentVariables field of the request body of https://docs.apify.com/api/v2/act-versions-post#request could be used for this.
• Motivation is being able to pass build args to the Dockerfile without touching the Apify Console
  • This is helpful when building Actors via CI