Change records "proxied" default

### Describe the Feature

```tf
proxied = lookup(each.value, "proxied", false)
```
- https://github.com/cloudposse/terraform-cloudflare-zone/blob/3073cc39498d44ec44f023ffe1ec8d03d664ebf7/main.tf#L42

I would like to change proxied to `true` by default, as most of the records are proxied.

### Expected Behavior

Maybe introduce a new variable: `local.records_proxied_default`?

### Use Case

Reduce duplication.

Start with main.tf around the records definition at line 42 and review how the proxied value is currently looked up. Make the default behavior true, potentially through the proposed local.records_proxied_default, and verify that record configurations no longer need to repeat proxied=true.

Written by the indexing model from the issue text.