dashboard: CPU, memory, diskIO and traffic on the footer (#15950)

* dashboard: footer, deep state update

* dashboard: resolve asset path

* dashboard: prevent state update on every reconnection

* dashboard: fix linter issue

* dashboard, cmd: minor UI fix, include commit hash

* dashboard: gitCommit renamed to commit

* dashboard: move the geth version to the right, make commit optional

* dashboard: memory, traffic and CPU on footer

* dashboard: fix merge

* dashboard: CPU, diskIO on footer

* dashboard: rename variables, use group declaration

* dashboard: docs

vendor/github.com/elastic/gosigar/sigar_unix.go

@@ -0,0 +1,69 @@
+// Copyright (c) 2012 VMware, Inc.
+
+// +build darwin freebsd linux
+
+package gosigar
+
+import (
+	"syscall"
+	"time"
+
+	"golang.org/x/sys/unix"
+)
+
+func (self *FileSystemUsage) Get(path string) error {
+	stat := syscall.Statfs_t{}
+	err := syscall.Statfs(path, &stat)
+	if err != nil {
+		return err
+	}
+
+	self.Total = uint64(stat.Blocks) * uint64(stat.Bsize)
+	self.Free = uint64(stat.Bfree) * uint64(stat.Bsize)
+	self.Avail = uint64(stat.Bavail) * uint64(stat.Bsize)
+	self.Used = self.Total - self.Free
+	self.Files = stat.Files
+	self.FreeFiles = uint64(stat.Ffree)
+
+	return nil
+}
+
+func (r *Rusage) Get(who int) error {
+	ru, err := getResourceUsage(who)
+	if err != nil {
+		return err
+	}
+
+	uTime := convertRtimeToDur(ru.Utime)
+	sTime := convertRtimeToDur(ru.Stime)
+
+	r.Utime = uTime
+	r.Stime = sTime
+	r.Maxrss = int64(ru.Maxrss)
+	r.Ixrss = int64(ru.Ixrss)
+	r.Idrss = int64(ru.Idrss)
+	r.Isrss = int64(ru.Isrss)
+	r.Minflt = int64(ru.Minflt)
+	r.Majflt = int64(ru.Majflt)
+	r.Nswap = int64(ru.Nswap)
+	r.Inblock = int64(ru.Inblock)
+	r.Oublock = int64(ru.Oublock)
+	r.Msgsnd = int64(ru.Msgsnd)
+	r.Msgrcv = int64(ru.Msgrcv)
+	r.Nsignals = int64(ru.Nsignals)
+	r.Nvcsw = int64(ru.Nvcsw)
+	r.Nivcsw = int64(ru.Nivcsw)
+
+	return nil
+}
+
+func getResourceUsage(who int) (unix.Rusage, error) {
+	r := unix.Rusage{}
+	err := unix.Getrusage(who, &r)
+
+	return r, err
+}
+
+func convertRtimeToDur(t unix.Timeval) time.Duration {
+	return time.Duration(t.Nano())
+}