Add option to disable timestamp adjustment in grok parser (#5488)

plugins/parsers/grok/README.md

@@ -110,6 +110,9 @@ you will find the https://grokdebug.herokuapp.com application quite useful!
   ##   2. "Canada/Eastern"  -- Unix TZ values like those found in https://en.wikipedia.org/wiki/List_of_tz_database_time_zones
   ##   3. UTC               -- or blank/unspecified, will return timestamp in UTC
   grok_timezone = "Canada/Eastern"
+
+  ## When grok_unique_timestamp is set to "disable", timestamp will not incremented if there is a duplicate. Default is "auto"
+  # grok_unique_timestamp = "auto"
 ```
 
 #### Timestamp Examples

plugins/parsers/grok/parser.go

@@ -86,6 +86,9 @@ type Parser struct {
 	Timezone string
 	loc      *time.Location
 
+	// UniqueTimestamp when set to "disable", timestamp will not incremented if there is a duplicate.
+	UniqueTimestamp string
+
 	// typeMap is a map of patterns -> capture name -> modifier,
 	//   ie, {
 	//          "%{TESTLOG}":
@@ -134,6 +137,10 @@ func (p *Parser) Compile() error {
 		return err
 	}
 
+	if p.UniqueTimestamp == "" {
+		p.UniqueTimestamp = "auto"
+	}
+
 	// Give Patterns fake names so that they can be treated as named
 	// "custom patterns"
 	p.NamedPatterns = make([]string, 0, len(p.Patterns))
@@ -358,6 +365,10 @@ func (p *Parser) ParseLine(line string) (telegraf.Metric, error) {
 		return nil, fmt.Errorf("grok: must have one or more fields")
 	}
 
+	if p.UniqueTimestamp != "auto" {
+		return metric.New(p.Measurement, tags, fields, timestamp)
+	}
+
 	return metric.New(p.Measurement, tags, fields, p.tsModder.tsMod(timestamp))
 }