fix: Update examples

[kirklandnuts]

Summary

Fixes small errors in the examples:

1. In all examples, the global module should have lacework_account specified. This is not a required variable, but the default value ("") doesn't make sense here.
2. In the tenant-single-region example, the module is missing the region attribute. By default, this causes AWLS to be deployed in US West 2.
3. In the custom-vnet example, the vnet resource should have subnet.address_prefixes (list[str]) instead of subnet.address_prefix (str).

How did you test this change?

Changes 1 and 2 match our internal deployments. No functional changes here, just specifying explicit values instead of relying on defaults.

For the custom-vnet changes, I successfully deployed the azure vnet on its own — it errored with the previous syntax.

Issue

N/A