[Connections] Consider null and unknown as valid in url string validator

[fridgepoet]

An issue was raised that string validation was returning an error on the result of each.value from for_each. In the following example, existing string validation was rejecting each.value because it is null/unknown.
This PR allows for null/unknown values in our string validation and adds tests using the for_each.

Example:

locals {
  jobs = [
    { name = "test", url = "<some valid url>" }
  ]
}

resource "grafana_connections_metrics_endpoint_scrape_job" "valid_url" {
  for_each = { for j in local.jobs : j.name => j.url }
  stack_id = "1"
  name = each.key
  enabled = true
  authentication_method = "bearer"
  authentication_bearer_token = "<some valid token>"
  url = each.value
}

Running terraform plan before would result in:

╷
│ Error: value must be valid URL with HTTPS
│
│   with grafana_connections_metrics_endpoint_scrape_job.valid_url,
│   on main.tf line 19, in resource "grafana_connections_metrics_endpoint_scrape_job" "valid_url":
│   19:   url = each.value
│
│ A valid URL is required.
│
│ Given Value: ""
│ 

Running terraform plan with the changes in this PR now results in:

Terraform will perform the following actions:

  # grafana_connections_metrics_endpoint_scrape_job.valid_url["test"] will be created
  + resource "grafana_connections_metrics_endpoint_scrape_job" "valid_url" {
      + authentication_bearer_token = (sensitive value)
      + authentication_method       = "bearer"
      + enabled                     = true
      + id                          = (known after apply)
      + name                        = "test"
      + scrape_interval_seconds     = 60
      + stack_id                    = "1"
      + url                         = "<some valid url>"
    }

Plan: 1 to add, 0 to change, 0 to destroy.

Applying is successful and one can see the job in the UI:

Fixes https://github.com/grafana/support-escalations/issues/13779

[github-actions]

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.

[matthewnolf]

So with the early break on IsNull or IsUnknown, we still do the validation at a later point?

[fridgepoet]

Yes, this example provides an empty string so it continues to

terraform-provider-grafana/internal/resources/connections/resources.go

Line 42 in 340c690

response.Diagnostics.AddAttributeError(

(unit test on empty string: https://github.com/grafana/terraform-provider-grafana/blob/e5e3eb356e1d2e4c99b3d862dee1889ffd5ca9af/internal/resources/connections/resources_test.go#L34-L33)

[Duologic]

I think the tests are fixed after a rebase.

[matthewnolf]

LGTM