fix: remove inline GC and schedule a background task instead (#1610)

* fix: remove inline GC and set a default value of gc interval

- remove inline GC
- add a default value of GC interval
- run the GC periodically by default with the default value if no interval provided
- generate GC tasks with a random delay(0-30s) between
- add IsReady() method to scheduler.TaskGenerator interface

Signed-off-by: Andreea-Lupu <andreealupu1470@yahoo.com>

* ci: add test for gc with short interval

Signed-off-by: Andreea-Lupu <andreealupu1470@yahoo.com>

---------

Signed-off-by: Andreea-Lupu <andreealupu1470@yahoo.com>

pkg/extensions/scrub/scrub_test.go

@@ -46,6 +46,7 @@ func TestScrubExtension(t *testing.T) {
 
 		conf.Storage.RootDirectory = dir
 		conf.Storage.Dedupe = false
+		conf.Storage.GC = false
 
 		substore := config.StorageConfig{RootDirectory: subdir}
 		conf.Storage.SubPaths = map[string]config.StorageConfig{"/a": substore}
@@ -89,6 +90,7 @@ func TestScrubExtension(t *testing.T) {
 
 		conf.Storage.RootDirectory = dir
 		conf.Storage.Dedupe = false
+		conf.Storage.GC = false
 
 		conf.Log.Output = logFile.Name()
 		trueValue := true
@@ -137,6 +139,7 @@ func TestScrubExtension(t *testing.T) {
 
 		conf.Storage.RootDirectory = dir
 		conf.Storage.Dedupe = false
+		conf.Storage.GC = false
 
 		conf.Log.Output = logFile.Name()
 		trueValue := true