Env Var Interpolation Off By Default.Breaking

Environment variable interpolation in configuration files is now disabled by default. Previously, Vector interpolated ${VAR} references in config files automatically. To restore the previous behavior, pass --dangerously-allow-env-var-interpolation (or set VECTOR_DANGEROUSLY_ALLOW_ENV_VAR_INTERPOLATION=true). The --disable-env-var-interpolation flag and VECTOR_DISABLE_ENV_VAR_INTERPOLATION environment variable have been removed.

authors: thomasqueirozb