cmd, dashboard, log: log collection and exploration (#17097)

* cmd, dashboard, internal, log, node: logging feature

* cmd, dashboard, internal, log: requested changes

* dashboard, vendor: gofmt, govendor, use vendored file watcher

* dashboard, log: gofmt -s -w, goimports

* dashboard, log: gosimple

log/logger.go

@@ -11,6 +11,7 @@ import (
 const timeKey = "t"
 const lvlKey = "lvl"
 const msgKey = "msg"
+const ctxKey = "ctx"
 const errorKey = "LOG15_ERROR"
 const skipLevel = 2
 
@@ -101,6 +102,7 @@ type RecordKeyNames struct {
 	Time string
 	Msg  string
 	Lvl  string
+	Ctx  string
 }
 
 // A Logger writes key/value pairs to a Handler
@@ -139,6 +141,7 @@ func (l *logger) write(msg string, lvl Lvl, ctx []interface{}, skip int) {
 			Time: timeKey,
 			Msg:  msgKey,
 			Lvl:  lvlKey,
+			Ctx:  ctxKey,
 		},
 	})
 }