Rename purger target flag (grafana#2777)

* rename purger target flag

Signed-off-by: Sandeep Sukhani <sandeep.d.sukhani@gmail.com>

* fix a flaky test in purger

Signed-off-by: Sandeep Sukhani <sandeep.d.sukhani@gmail.com>

* update changelog

Signed-off-by: Sandeep Sukhani <sandeep.d.sukhani@gmail.com>

purger/purger_test.go

@@ -4,7 +4,6 @@ import (
 	"context"
 	"fmt"
 	"sort"
-	"strings"
 	"testing"
 	"time"
 
@@ -392,27 +391,7 @@ func TestPurger_Metrics(t *testing.T) {
 		chunkStore.Stop()
 	}()
 
-	// start loop to load requests
-	require.NoError(t, services.StartAndAwaitRunning(context.Background(), purger))
-
-	// no delete requests for processing so age and pending request is 0 while we have successfully attempted loading request once.
-	require.NoError(t, testutil.GatherAndCompare(registry, strings.NewReader(
-		`
-			# HELP cortex_purger_load_pending_requests_attempts_total Number of attempts that were made to load pending requests with status
-			# TYPE cortex_purger_load_pending_requests_attempts_total counter
-			cortex_purger_load_pending_requests_attempts_total{status="success"} 1
-			# HELP cortex_purger_oldest_pending_delete_request_age_seconds Age of oldest pending delete request in seconds
-			# TYPE cortex_purger_oldest_pending_delete_request_age_seconds gauge
-			cortex_purger_oldest_pending_delete_request_age_seconds 0
-			# HELP cortex_purger_pending_delete_requests_count Count of requests which are in process or are ready to be processed
-			# TYPE cortex_purger_pending_delete_requests_count gauge
-			cortex_purger_pending_delete_requests_count 0
-		`),
-		"cortex_purger_load_pending_requests_attempts_total",
-		"cortex_purger_oldest_pending_delete_request_age_seconds",
-		"cortex_purger_pending_delete_requests_count",
-	))
-
+	// add delete requests without starting purger loops to load and process delete requests.
 	// add delete request whose createdAt is now
 	err := deleteStore.AddDeleteRequest(context.Background(), userID, model.Time(0).Add(24*time.Hour),
 		model.Time(0).Add(2*24*time.Hour), []string{"foo"})
@@ -435,6 +414,9 @@ func TestPurger_Metrics(t *testing.T) {
 	require.InDelta(t, float64(3*86400), testutil.ToFloat64(purger.metrics.oldestPendingDeleteRequestAgeSeconds), 1)
 	require.Equal(t, float64(2), testutil.ToFloat64(purger.metrics.pendingDeleteRequestsCount))
 
+	// start loop to process requests
+	require.NoError(t, services.StartAndAwaitRunning(context.Background(), purger))
+
 	// wait until purger_delete_requests_processed_total starts to show up.
 	test.Poll(t, 2*time.Second, 1, func() interface{} {
 		count, err := testutil.GatherAndCount(registry, "cortex_purger_delete_requests_processed_total")