add org_id to the resource grafana_user

[valentin-naina]

Currently, this version does not allow the resource "grafana_user" to assign the user to an organization. This commit adds this feature.

[julienduchesne]

The idea seems good to me. Though:

1. We should also get this information when we read the user
2. It should also be tested (adding the attribute to verified attributes in the acceptance tests)

To make it clear, it is ok to have the Org ID here because users is an admin resource. Explained here: https://github.com/grafana/terraform-provider-grafana/issues/59#issuecomment-996935572

[inkel]

Also please note that the documentation is out of date, please run go generate to update the docs.

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[julienduchesne]

I'll close this because it's been inactive for so long. Managing an org's users is already possible using the grafana_organization resource: https://registry.terraform.io/providers/grafana/grafana/latest/docs/resources/organization