SLO: Support Custom UUIDs in Terraform Provider

[elainevuong]

Adds support for setting custom UUIDs on the Terraform resources for SLO
This behaviour is already enabled in the API

Fixes #2316

[github-actions]

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[ellisda]

LGTM (but I'm not qualified here to approve proper) - I left a couple of questions

[ellisda]

question: are we using this combination of "computed=true, optional=true" elsewhere in SLO or grafana?

From a GPT search it seems this combination does what we want

Key Characteristics of Computed fields:

Provider-Generated: The value is not known until the resource is created or updated by the provider.

Read-Only in Configuration: Users typically do not set values for computed attributes in their .tf files. If they do, the provider will overwrite it with the computed value.

Can be Optional: An attribute can be both Optional and Computed. This allows a user to optionally provide a value. If a value is provided, it will be used; if not, the provider will compute a value.

[elainevuong]

yep - computed: true, optional: true is used in Grafana, and you can see the same use case - the UID is automatically generated unless it is specified during the panel creation. You can see it in here in the resourceLibraryPanel in our Grafana Terraform Provider

func resourceLibraryPanel() *common.Resource {
	schema := &schema.Resource{

		Description: Manages Grafana library panels.
		...
		Schema: map[string]*schema.Schema{
			"org_id": orgIDAttribute(),
			"uid": {
				Type:     schema.TypeString,
				Computed: true,
				Optional: true,
				Description: "The unique identifier (UID) of a library panel uniquely identifies library panels between multiple Grafana installs. " +
					"It’s automatically generated unless you specify it during library panel creation." +
					"The UID provides consistent URLs for accessing library panels and when syncing library panels between multiple Grafana installs.",
			},

For your comment below - I think the ForceNew could potentially hurt the customer. ForceNew means that if the field is modified, the resource will be destroyed and re-created. Our API already has a preventative mechanism for this - we don't allow PUTs to change the SLO UUIDs, so I agree with your thoughts and the ForceNew isn't needed here. Will remove, thanks! 👍