contrib: expand Windows mixin rules and publish runbooks (#2575)

Signed-off-by: Jan-Otto Kröpke <mail@jkroepke.de>

docs/runbooks/windowsdiskalmostfull.md

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+---
+title: WindowsDiskAlmostFull
+---
+
+## Meaning
+
+The volume's free space remains below a configured threshold for 15 minutes.
+Defaults are 10% for warning and 5% for critical. Both severity levels fire below
+the critical threshold unless Alertmanager inhibition suppresses the warning.
+Windows can delay the underlying space counters by 10–15 minutes.
+
+## Impact
+
+Applications may fail to write data or logs. Low free space can prevent updates,
+pagefile growth, database operations, and normal operating system behavior.
+
+## Diagnosis
+
+1. Use the `volume` label to identify the affected filesystem and inspect
+   `windows:logical_disk_free:ratio` and `windows_logical_disk_free_bytes`.
+2. Verify current capacity locally; the exporter counters may lag:
+
+   ```powershell
+   Get-Volume | Select-Object DriveLetter, FileSystemLabel, SizeRemaining, Size
+   ```
+
+3. Identify growing logs, temporary files, backups, database files, and application
+   data. Check retention policies and recent jobs.
+4. Consult [WindowsDiskFillingUp](../windowsdiskfillingup/) when free space is
+   declining rapidly.
+
+## Mitigation
+
+Expand the volume or remove files through the owning application's supported
+retention and cleanup process. Preserve required data and backups; avoid manually
+deleting database files or Windows system files. Reduce incoming writes if the
+volume may fill before capacity is restored. Verify space locally and allow the
+Windows counters to refresh before expecting the alert to resolve.