Add common provider headers to cloud-provider-client

[thepalbi]

This PR adds provider headers the cloud-provider-client. This are basically:

• Grafana-Terraform-Provider: true if request coming from provider, allows us in the API to understand a request comes from the provider
• Grafana-Terraform-Provider-Version: contains version of provider, might be useful to propagate it through context and log it to debug provider issues

Also, once we have this, we can identify from which client a request is coming from, and then, store the "provenance" of a resource. Using here the same concept SLO uses https://github.com/grafana/slo/blob/346637b4ce113db1bc910f46fc397c72943e3426/pkg/api/slo.go#L410, which sounds just right.

[github-actions[bot]]

In order to lower resource usage and have a faster runtime, PRs will not run Cloud tests automatically. To do so, a Grafana Labs employee must trigger the cloud acceptance tests workflow manually.

[thepalbi]

@Duologic changes applied!