chore: update .goreleaser-plugin.yaml to non-deprecated archives schema

[scotwells]

Problem

.goreleaser-plugin.yaml (the datumctl-compute release config) uses keys that are deprecated in goreleaser v2 and emit warnings on every release:

• archives.format
• archives.format_overrides.format
• archives.builds

These still function on goreleaser 2.16, but will break when a future goreleaser major drops them — at which point CLI plugin releases would fail.

Desired outcome

Migrate the config to the current archives schema (e.g. formats:, ids:, and the new format_overrides shape) per https://goreleaser.com/deprecations so goreleaser release runs without deprecation warnings. Verify a snapshot build (goreleaser build --snapshot --clean --config .goreleaser-plugin.yaml) still produces the same six platform archives with identical names.

Context

• Surfaced while cutting the v0.8.0-dev.2 plugin pre-release.