set feature gate as beta

Author: rogercoll

receiver/hostmetricsreceiver/internal/scraper/memoryscraper/memory_scraper_linux.go

@@ -15,7 +15,7 @@ import (
 
 var useMemAvailable = featuregate.GlobalRegistry().MustRegister(
 	"receiver.hostmetricsreceiver.UseLinuxMemAvailable",
-	featuregate.StageAlpha,
+	featuregate.StageBeta,
 	featuregate.WithRegisterFromVersion("v0.136.0"),
 	featuregate.WithRegisterDescription("When enabled, the used value for the system.memory.usage and system.memory.utilization metrics will be based on the Linux kernel’s MemAvailable statistic instead of MemFree, Buffers, and Cached."),
 	featuregate.WithRegisterReferenceURL("https://github.com/open-telemetry/opentelemetry-collector-contrib/issues/42221"),