`betteruptime_status_page` resource creation fails by default on Free accounts because `subscribable` (paid feature) is `true` by default

[ricardbejarano]

suscribable is true by default on betteruptime_status_page resources, which is a paid feature, thus breaking resource creation for Free users:

terraform-provider-better-uptime/internal/provider/resource_status_page.go

Line 64 in 372c16b

Default: true,

Perhaps not setting a default value is a better choice.

[ricardbejarano]

Raised #12 which solves this.

Thanks!