Ability to import a `wireguard_asymmetric_key` & `wireguard_preshared_key`

[leonsmith]

I know you can target apply & manually adjust the state file to achieve the same thing but it would be nice if you could import a pre-existing wireguard_asymmetric_key or wireguard_preshared_key

[leonsmith]

Might have a go at implementing it myself this week in my spare time 👍

[OJFord]

Thank you, yes, I've definitely intended to do this, PR more than welcome but no pressure, I will get to it otherwise.

[fllaca]

hi @leonsmith @OJFord ! I implemented this feature in https://github.com/OJFord/terraform-provider-wireguard/pull/38 , please have a look :pray: .

Thanks for this project!