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.go

@@ -0,0 +1,70 @@
+package diagnostic
+
+import "context"
+
+type DiskVolumeInformation struct {
+	Name        string `json:"name"`        // represents the filesystem in linux/macos or device name in windows
+	SizeMaximum uint64 `json:"sizeMaximum"` // represents the maximum size of the disk in kilobytes
+	SizeCurrent uint64 `json:"sizeCurrent"` // represents the current size of the disk in kilobytes
+}
+
+func NewDiskVolumeInformation(name string, maximum, current uint64) *DiskVolumeInformation {
+	return &DiskVolumeInformation{
+		name,
+		maximum,
+		current,
+	}
+}
+
+type SystemInformation struct {
+	MemoryMaximum         uint64                   `json:"memoryMaximum"`         // represents the maximum memory of the system in kilobytes
+	MemoryCurrent         uint64                   `json:"memoryCurrent"`         // represents the system's memory in use in kilobytes
+	FileDescriptorMaximum uint64                   `json:"fileDescriptorMaximum"` // represents the maximum number of file descriptors of the system
+	FileDescriptorCurrent uint64                   `json:"fileDescriptorCurrent"` // represents the system's file descriptors in use
+	OsSystem              string                   `json:"osSystem"`              // represents the operating system name i.e.: linux, windows, darwin
+	HostName              string                   `json:"hostName"`              // represents the system host name
+	OsVersion             string                   `json:"osVersion"`             // detailed information about the system's release version level
+	OsRelease             string                   `json:"osRelease"`             // detailed information about the system's release
+	Architecture          string                   `json:"architecture"`          // represents the system's hardware platform i.e: arm64/amd64
+	CloudflaredVersion    string                   `json:"cloudflaredVersion"`    // the runtime version of cloudflared
+	Disk                  []*DiskVolumeInformation `json:"disk"`
+}
+
+func NewSystemInformation(
+	memoryMaximum,
+	memoryCurrent,
+	filesMaximum,
+	filesCurrent uint64,
+	osystem,
+	name,
+	osVersion,
+	osRelease,
+	architecture,
+	cloudflaredVersion string,
+	disk []*DiskVolumeInformation,
+) *SystemInformation {
+	return &SystemInformation{
+		memoryMaximum,
+		memoryCurrent,
+		filesMaximum,
+		filesCurrent,
+		osystem,
+		name,
+		osVersion,
+		osRelease,
+		architecture,
+		cloudflaredVersion,
+		disk,
+	}
+}
+
+type SystemCollector interface {
+	// If the collection is successful it will return `SystemInformation` struct,
+	// an empty string, and a nil error.
+	// In case there is an error a string with the raw data will be returned
+	// however the returned string not contain all the data points.
+	//
+	// This function expects that the caller sets the context timeout to prevent
+	// long-lived collectors.
+	Collect(ctx context.Context) (*SystemInformation, string, error)
+}