Configure user agent to identify Pulumi

[ringods]

Check whether and/or how to indicate that requests using this provider come from Pulumi.

[danielrbradley]

Updating this here:

https://github.com/scaleway/terraform-provider-scaleway/blob/ab73459f5d127fd0d758a2ba5a569c7d3a4633d0/internal/meta/meta.go#L197-L205