ci: expand Windows feature fixtures and test Server 2022 (#2503)

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Jan-Otto Kröpke <mail@jkroepke.de>

docs/ci-testing.md

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+# Windows feature tests
+
+The CI Windows job prepares real Windows roles and workloads before running
+`go test -json -count=1 -race -timeout=10m ./...`. Collector tests validate the
+metrics from those workloads. A final exporter smoke check builds and starts the
+binary, requests `/metrics` once, and checks for a nonempty HTTP 200 response.
+
+The job runs on Windows Server 2022; Server 2025 runners take much longer to
+provision the same fixtures. It provisions Containers, Hyper-V, SQL Server
+Express, IIS, SMTP, MSMQ, NPS, FSRM, SMB, DNS, DHCP, a workgroup failover
+cluster, printer and storage fixtures, unlocked and locked BitLocker volumes,
+and an authenticated RDP session.
+
+`WINDOWS_EXPORTER_TEST_COLLECTORS` lists required collectors. Their tests fail
+when setup is missing or collection fails instead of skipping. Fixture assertions
+check known instances, including the active RDP user's session and SQL database.
+RemoteFX is required when both network and graphics instances are available.
+
+Each Windows job publishes a feature table in its Actions summary and a
+`windows-test-results-<OS>` artifact containing `feature-summary.md`, structured
+Go test events, readable test output, and setup diagnostics. The table distinguishes
+required fixtures, unavailable collectors, and empty optional instance groups.
+This records Windows feature availability rather than Go statement coverage.