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>

examples/config-conformance.json

@@ -2,8 +2,8 @@
   "distSpecVersion": "1.1.0-dev",
   "storage": {
     "rootDirectory": "/tmp/zot",
-    "gc": false,
-    "dedupe": false
+    "gc": true,
+    "dedupe": true
   },
   "http": {
     "address": "0.0.0.0",

examples/config-gc-bench.json

@@ -0,0 +1,17 @@
+{
+    "distSpecVersion": "1.1.0-dev",
+    "storage": {
+        "rootDirectory": "/tmp/zot",
+        "gc": true,
+        "gcDelay": "10s",
+        "gcInterval": "1s"
+    },
+    "http": {
+        "address": "127.0.0.1",
+        "port": "8080"
+    },
+    "log": {
+        "level": "debug",
+        "output": "/dev/null"
+    }
+}