TUN-8731: Implement diag/system endpoint

## Summary
This PR will add a new endpoint, "diag/system" to the metrics server that collects system information from different operating systems.

Closes TUN-8731

diagnostic/system_collector_windows.go

@@ -0,0 +1,153 @@
+//go:build windows
+
+package diagnostic
+
+import (
+	"context"
+	"fmt"
+	"os/exec"
+	"strconv"
+)
+
+const kiloBytesScale = 1.0 / 1024
+
+type SystemCollectorImpl struct {
+	version string
+}
+
+func NewSystemCollectorImpl(
+	version string,
+) *SystemCollectorImpl {
+	return &SystemCollectorImpl{
+		version,
+	}
+}
+func (collector *SystemCollectorImpl) Collect(ctx context.Context) (*SystemInformation, string, error) {
+	memoryInfo, memoryInfoRaw, memoryInfoErr := collectMemoryInformation(ctx)
+	disks, disksRaw, diskErr := collectDiskVolumeInformation(ctx)
+	osInfo, osInfoRaw, osInfoErr := collectOSInformation(ctx)
+
+	if memoryInfoErr != nil {
+		raw := RawSystemInformation(osInfoRaw, memoryInfoRaw, "", disksRaw)
+		return nil, raw, memoryInfoErr
+	}
+
+	if diskErr != nil {
+		raw := RawSystemInformation(osInfoRaw, memoryInfoRaw, "", disksRaw)
+		return nil, raw, diskErr
+	}
+
+	if osInfoErr != nil {
+		raw := RawSystemInformation(osInfoRaw, memoryInfoRaw, "", disksRaw)
+		return nil, raw, osInfoErr
+	}
+
+	return NewSystemInformation(
+		memoryInfo.MemoryMaximum,
+		memoryInfo.MemoryCurrent,
+		// For windows we leave both the fileDescriptorMaximum and fileDescriptorCurrent with zero
+		// since there is no obvious way to get this information.
+		0,
+		0,
+		osInfo.OsSystem,
+		osInfo.Name,
+		osInfo.OsVersion,
+		osInfo.OsRelease,
+		osInfo.Architecture,
+		collector.version,
+		disks,
+	), "", nil
+}
+
+func collectMemoryInformation(ctx context.Context) (*MemoryInformation, string, error) {
+	const (
+		memoryTotalPrefix     = "TotalVirtualMemorySize"
+		memoryAvailablePrefix = "FreeVirtualMemory"
+	)
+
+	command := exec.CommandContext(
+		ctx,
+		"powershell",
+		"-Command",
+		"Get-CimInstance -Class Win32_OperatingSystem | Select-Object FreeVirtualMemory, TotalVirtualMemorySize | Format-List",
+	)
+
+	stdout, err := command.Output()
+	if err != nil {
+		return nil, "", fmt.Errorf("error retrieving output from command '%s': %w", command.String(), err)
+	}
+
+	output := string(stdout)
+
+	// the result of the command above will return values in bytes hence
+	// they need to be converted to kilobytes
+	mapper := func(field string) (uint64, error) {
+		value, err := strconv.ParseUint(field, 10, 64)
+		return uint64(float64(value) * kiloBytesScale), err
+	}
+
+	memoryInfo, err := ParseMemoryInformationFromKV(output, memoryTotalPrefix, memoryAvailablePrefix, mapper)
+	if err != nil {
+		return nil, output, err
+	}
+
+	// returning raw output in case other collected information
+	// resulted in errors
+	return memoryInfo, output, nil
+}
+
+func collectDiskVolumeInformation(ctx context.Context) ([]*DiskVolumeInformation, string, error) {
+
+	command := exec.CommandContext(
+		ctx,
+		"powershell", "-Command", "Get-CimInstance -Class Win32_LogicalDisk | Select-Object DeviceID, Size, FreeSpace")
+
+	stdout, err := command.Output()
+	if err != nil {
+		return nil, "", fmt.Errorf("error retrieving output from command '%s': %w", command.String(), err)
+	}
+
+	output := string(stdout)
+
+	disks, err := ParseDiskVolumeInformationOutput(output, 2, kiloBytesScale)
+	if err != nil {
+		return nil, output, err
+	}
+
+	// returning raw output in case other collected information
+	// resulted in errors
+	return disks, output, nil
+}
+
+func collectOSInformation(ctx context.Context) (*OsInfo, string, error) {
+	const (
+		architecturePrefix = "OSArchitecture"
+		osSystemPrefix     = "Caption"
+		osVersionPrefix    = "Version"
+		osReleasePrefix    = "BuildNumber"
+		namePrefix         = "CSName"
+	)
+
+	command := exec.CommandContext(
+		ctx,
+		"powershell",
+		"-Command",
+		"Get-CimInstance -Class Win32_OperatingSystem | Select-Object OSArchitecture, Caption, Version, BuildNumber, CSName | Format-List",
+	)
+
+	stdout, err := command.Output()
+	if err != nil {
+		return nil, "", fmt.Errorf("error retrieving output from command '%s': %w", command.String(), err)
+	}
+
+	output := string(stdout)
+
+	osInfo, err := ParseWinOperatingSystemInfo(output, architecturePrefix, osSystemPrefix, osVersionPrefix, osReleasePrefix, namePrefix)
+	if err != nil {
+		return nil, output, err
+	}
+
+	// returning raw output in case other collected information
+	// resulted in errors
+	return osInfo, output, nil
+}