Improve queue & process & stacktrace (#24636)

Although some features are mixed together in this PR, this PR is not
that large, and these features are all related.

Actually there are more than 70 lines are for a toy "test queue", so
this PR is quite simple.

Major features:

1. Allow site admin to clear a queue (remove all items in a queue)
* Because there is no transaction, the "unique queue" could be corrupted
in rare cases, that's unfixable.
* eg: the item is in the "set" but not in the "list", so the item would
never be able to be pushed into the queue.
* Now site admin could simply clear the queue, then everything becomes
correct, the lost items could be re-pushed into queue by future
operations.
3. Split the "admin/monitor" to separate pages
4. Allow to download diagnosis report
* In history, there were many users reporting that Gitea queue gets
stuck, or Gitea's CPU is 100%
    * With diagnosis report, maintainers could know what happens clearly

The diagnosis report sample:
[gitea-diagnosis-20230510-192913.zip](11441346/gitea-diagnosis-20230510-192913.zip)
, use "go tool pprof profile.dat" to view the report.


Screenshots:


![image](320659b4-2eda-4def-8dc0-5ea08d578063)


![image](c5c46fae-9dc0-44ca-8cd3-57beedc5035e)


![image](6168a811-42a1-4e64-a263-0617a6c8c4fe)

---------

Co-authored-by: Jason Song <i@wolfogre.com>
Co-authored-by: Giteabot <teabot@gitea.io>

modules/queue/base_channel.go

@@ -87,7 +87,9 @@ func (q *baseChannel) PopItem(ctx context.Context) ([]byte, error) {
 func (q *baseChannel) HasItem(ctx context.Context, data []byte) (bool, error) {
 	q.mu.Lock()
 	defer q.mu.Unlock()
-
+	if !q.isUnique {
+		return false, nil
+	}
 	return q.set.Contains(string(data)), nil
 }
 
@@ -107,7 +109,9 @@ func (q *baseChannel) Close() error {
 	defer q.mu.Unlock()
 
 	close(q.c)
-	q.set = container.Set[string]{}
+	if q.isUnique {
+		q.set = container.Set[string]{}
+	}
 
 	return nil
 }
@@ -119,5 +123,9 @@ func (q *baseChannel) RemoveAll(ctx context.Context) error {
 	for q.c != nil && len(q.c) > 0 {
 		<-q.c
 	}
+
+	if q.isUnique {
+		q.set = container.Set[string]{}
+	}
 	return nil
 }