Allow disabling VPC interface endpoints only

[evan10s]

Describe the outcome you'd like

VPC interface endpoints are pretty expensive (>50% of our AFT costs). It would be nice to be able to disable the interface endpoints only; currently, setting var.aft_vpc_endpoints to false will also disable the VPC Gateway endpoints, which are free (so there's not really a reason to disable them).

Is your feature request related to a problem you are currently experiencing? If so, please describe.

While not a huge deal in the grand scheme of things, some people might decide the cost tradeoff to have VPC interface endpoints for every AWS service used by AFT is not worth it. It would be nice to have the choice to disable the VPC interface endpoints if you so decide. But in doing so, currently, the free Gateway endpoints would also be disabled, and we'd like to keep those around.

Additional context

n/a