Fix goroutine leak on initialization failures of log input (#12125) (#12144)

Outlets are created during log input initialization, and if it
fails they were never freed. Handle this case.

(cherry picked from commit f2473d2)

Author: jsoriano

CHANGELOG.next.asciidoc

@@ -44,6 +44,7 @@ https://github.com/elastic/beats/compare/v6.7.2...6.8[Check the HEAD diff]
 
 - Fix goroutine leak happening when harvesters are dynamically stopped. {pull}11263[11263]
 - Fix initialization of the TCP input logger. {pull}11605[11605]
+- Fix goroutine leak caused on initialization failures of log input. {pull}12125[12125]
 - Fix memory leak in Filebeat pipeline acker. {pull}12063[12063]
 
 *Heartbeat*

filebeat/input/log/input.go

@@ -76,6 +76,12 @@ func NewInput(
 	outlet channel.Connector,
 	context input.Context,
 ) (input.Input, error) {
+	cleanupNeeded := true
+	cleanupIfNeeded := func(f func() error) {
+		if cleanupNeeded {
+			f()
+		}
+	}
 
 	// Note: underlying output.
 	//  The input and harvester do have different requirements
@@ -87,11 +93,13 @@ func NewInput(
 	if err != nil {
 		return nil, err
 	}
+	defer cleanupIfNeeded(out.Close)
 
 	// stateOut will only be unblocked if the beat is shut down.
 	// otherwise it can block on a full publisher pipeline, so state updates
 	// can be forwarded correctly to the registrar.
 	stateOut := channel.CloseOnSignal(channel.SubOutlet(out), context.BeatDone)
+	defer cleanupIfNeeded(stateOut.Close)
 
 	meta := context.Meta
 	if len(meta) == 0 {
@@ -137,6 +145,7 @@ func NewInput(
 
 	logp.Info("Configured paths: %v", p.config.Paths)
 
+	cleanupNeeded = false
 	return p, nil
 }