Add data source with an unstable ID

[paddycarver]

Add a data source without a stable ID, that changes its ID every single call. Reportedly, this should make diffs messier.

[kmoe]

Relevant: hashicorp/terraform-plugin-sdk#586

[bflad]

(Closing issues that likely won't get actioned anytime soon.) We can reopen if the external acceptance testing is required.

[github-actions]

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