Since an early version of Terraform, the `destroy` command has always
had the `-force` flag to allow an auto approval of the interactive
prompt. 0.11 introduced `-auto-approve` as default to `false` when using
the `apply` command.

The `-auto-approve` flag was introduced to reduce ambiguity of it's
function, but the `-force` flag was never updated for a destroy.

People often use wrappers when automating commands in Terraform, and the
inconsistency between `apply` and `destroy` means that additional logic
must be added to the wrappers to do similar functions. Both commands are
more or less able to run with similar syntax, and also heavily share
their code.

This commit updates the command in `destroy` to use the `-auto-approve` flag
making working with the Terraform CLI a more consistent experience.

We leave in `-force` in `destroy` for the time-being and flag it as
deprecated to ensure a safe switchover period.