add some default setting mentions in doc

Author: jotak

docs/api.md

@@ -34,7 +34,7 @@ Following is the supported API format for prometheus encode:
                  buckets: histogram buckets
                  valueScale: scale factor of the value (MetricVal := FlowVal / Scale)
          prefix: prefix added to each metric name
-         expiryTime: time duration of no-flow to wait before deleting prometheus data item
+         expiryTime: time duration of no-flow to wait before deleting prometheus data item (default: 2m)
          maxMetrics: maximum number of metrics to report (default: unlimited)
 </pre>
 ## Kafka encode API
@@ -458,8 +458,8 @@ Following is the supported API format for writing metrics to an OpenTelemetry co
                  flatten: list fields to be flattened
                  buckets: histogram buckets
                  valueScale: scale factor of the value (MetricVal := FlowVal / Scale)
-         pushTimeInterval: how often should metrics be sent to collector:
-         expiryTime: time duration of no-flow to wait before deleting data item
+         pushTimeInterval: how often should metrics be sent to collector (default: 20s)
+         expiryTime: time duration of no-flow to wait before deleting data item (default: 2m)
 </pre>
 ## OpenTelemetry Traces API
 Following is the supported API format for writing traces to an OpenTelemetry collector:

pkg/api/encode_otlp.go

@@ -30,8 +30,8 @@ type EncodeOtlpMetrics struct {
 	*OtlpConnectionInfo `json:",inline" doc:"OpenTelemetry connection info; includes:"`
 	Prefix              string       `yaml:"prefix,omitempty" json:"prefix,omitempty" doc:"prefix added to each metric name"`
 	Metrics             MetricsItems `yaml:"metrics,omitempty" json:"metrics,omitempty" doc:"list of metric definitions, each includes:"`
-	PushTimeInterval    Duration     `yaml:"pushTimeInterval,omitempty" json:"pushTimeInterval,omitempty" doc:"how often should metrics be sent to collector:"`
-	ExpiryTime          Duration     `yaml:"expiryTime,omitempty" json:"expiryTime,omitempty" doc:"time duration of no-flow to wait before deleting data item"`
+	PushTimeInterval    Duration     `yaml:"pushTimeInterval,omitempty" json:"pushTimeInterval,omitempty" doc:"how often should metrics be sent to collector (default: 20s)"`
+	ExpiryTime          Duration     `yaml:"expiryTime,omitempty" json:"expiryTime,omitempty" doc:"time duration of no-flow to wait before deleting data item (default: 2m)"`
 }
 
 type OtlpConnectionInfo struct {

pkg/api/encode_prom.go

@@ -26,7 +26,7 @@ type PromEncode struct {
 	*PromConnectionInfo `json:",inline,omitempty" doc:"Prometheus connection info (optional); includes:"`
 	Metrics             MetricsItems `yaml:"metrics,omitempty" json:"metrics,omitempty" doc:"list of prometheus metric definitions, each includes:"`
 	Prefix              string       `yaml:"prefix,omitempty" json:"prefix,omitempty" doc:"prefix added to each metric name"`
-	ExpiryTime          Duration     `yaml:"expiryTime,omitempty" json:"expiryTime,omitempty" doc:"time duration of no-flow to wait before deleting prometheus data item"`
+	ExpiryTime          Duration     `yaml:"expiryTime,omitempty" json:"expiryTime,omitempty" doc:"time duration of no-flow to wait before deleting prometheus data item (default: 2m)"`
 	MaxMetrics          int          `yaml:"maxMetrics,omitempty" json:"maxMetrics,omitempty" doc:"maximum number of metrics to report (default: unlimited)"`
 }