SLO: Implements SLO Datasource and SLO Resource

[elainevuong]

This PR implements a SLO Datasource (READ) and a SLO Resource (CRUD + Import) to the Grafana Terraform Provider.

Needs to be reviewed in conjunction with this PR on the Grafana Go API Client

For anyone who wants to test this on sloapp, feel free to check out the instructions within slo-testing-README.md within the slo_testing directory.

Detailed steps are provided for testing the TF Provider CRUD and Import Functionality.

[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 promote the Drone build.

For maintainers, it's better to run only the Cloud tests you need, rather than all of them. You can do so by setting the following parameter when promoting:

TESTARGS='-run=<testname>'

[elainevuong]

Latest look at our HCL Schema is here for anyone that is curious:

We will stick with a nested structure, and I've extracted out a string that specifies our query type. Anything other than the string "freeform" will throw a validation error on the TF Provider side indicating that the query type hasn't been implemented yet.

resource "grafana_slo" "test" {
  name        = "Terraform Testing"
  description = "Terraform Description"
  query {
    freeformquery = "sum(rate(apiserver_request_total{code!=\"500\"}[$__rate_interval])) / sum(rate(apiserver_request_total[$__rate_interval]))"
    type          = "freeform"
  }
  objectives {
    value  = 0.995
    window = "30d"
  }
  labels {
    key   = "custom"
    value = "value"
  }
  alerting {
    fastburn {
      annotations {
        key   = "name"
        value = "Critical - SLO Burn Rate Alert"
      }
      labels {
        key   = "type"
        value = "slo"
      }
    }

    slowburn {
      annotations {
        key   = "name"
        value = "Warning - SLO Burn Rate Alert"
      }
      labels {
        key   = "type"
        value = "slo"
      }
    }
  }
}

[elainevuong]

hey @joeblubaugh - do you mind deploying the latest version of our SLO Plugin to the terraformprovidergrafana2 stack.

Once that's done, the tests should pass, and you can start your review.

[julienduchesne]

I have some initial comments. Some of them imply pretty big changes (simplifying the code a bit) so I'd like to give another review after you've looked over my comments

[julienduchesne]

I don't know much about SLOs but the TF stuff looks great!

[julienduchesne]

I don't know much about SLOs but the TF stuff looks great!

[julienduchesne]

I don't know much about SLOs but the TF stuff looks great!

[joeblubaugh]

Please do "freeformquery" -> "freeform" in the schema. Otherwise looks great, and once done feel free to merge.