Rewrite queue (#24505)

# ⚠️ Breaking

Many deprecated queue config options are removed (actually, they should
have been removed in 1.18/1.19).

If you see the fatal message when starting Gitea: "Please update your
app.ini to remove deprecated config options", please follow the error
messages to remove these options from your app.ini.

Example:

```
2023/05/06 19:39:22 [E] Removed queue option: `[indexer].ISSUE_INDEXER_QUEUE_TYPE`. Use new options in `[queue.issue_indexer]`
2023/05/06 19:39:22 [E] Removed queue option: `[indexer].UPDATE_BUFFER_LEN`. Use new options in `[queue.issue_indexer]`
2023/05/06 19:39:22 [F] Please update your app.ini to remove deprecated config options
```

Many options in `[queue]` are are dropped, including:
`WRAP_IF_NECESSARY`, `MAX_ATTEMPTS`, `TIMEOUT`, `WORKERS`,
`BLOCK_TIMEOUT`, `BOOST_TIMEOUT`, `BOOST_WORKERS`, they can be removed
from app.ini.

# The problem

The old queue package has some legacy problems:

* complexity: I doubt few people could tell how it works.
* maintainability: Too many channels and mutex/cond are mixed together,
too many different structs/interfaces depends each other.
* stability: due to the complexity & maintainability, sometimes there
are strange bugs and difficult to debug, and some code doesn't have test
(indeed some code is difficult to test because a lot of things are mixed
together).
* general applicability: although it is called "queue", its behavior is
not a well-known queue.
* scalability: it doesn't seem easy to make it work with a cluster
without breaking its behaviors.

It came from some very old code to "avoid breaking", however, its
technical debt is too heavy now. It's a good time to introduce a better
"queue" package.

# The new queue package

It keeps using old config and concept as much as possible.

* It only contains two major kinds of concepts:
    * The "base queue": channel, levelqueue, redis
* They have the same abstraction, the same interface, and they are
tested by the same testing code.
* The "WokerPoolQueue", it uses the "base queue" to provide "worker
pool" function, calls the "handler" to process the data in the base
queue.
* The new code doesn't do "PushBack"
* Think about a queue with many workers, the "PushBack" can't guarantee
the order for re-queued unhandled items, so in new code it just does
"normal push"
* The new code doesn't do "pause/resume"
* The "pause/resume" was designed to handle some handler's failure: eg:
document indexer (elasticsearch) is down
* If a queue is paused for long time, either the producers blocks or the
new items are dropped.
* The new code doesn't do such "pause/resume" trick, it's not a common
queue's behavior and it doesn't help much.
* If there are unhandled items, the "push" function just blocks for a
few seconds and then re-queue them and retry.
* The new code doesn't do "worker booster"
* Gitea's queue's handlers are light functions, the cost is only the
go-routine, so it doesn't make sense to "boost" them.
* The new code only use "max worker number" to limit the concurrent
workers.
* The new "Push" never blocks forever
* Instead of creating more and more blocking goroutines, return an error
is more friendly to the server and to the end user.

There are more details in code comments: eg: the "Flush" problem, the
strange "code.index" hanging problem, the "immediate" queue problem.

Almost ready for review.

TODO:

* [x] add some necessary comments during review
* [x] add some more tests if necessary
* [x] update documents and config options
* [x] test max worker / active worker
* [x] re-run the CI tasks to see whether any test is flaky
* [x] improve the `handleOldLengthConfiguration` to provide more
friendly messages
* [x] fine tune default config values (eg: length?)

## Code coverage:

![image](https://user-images.githubusercontent.com/2114189/236620635-55576955-f95d-4810-b12f-879026a3afdf.png)

1 files changed, 8 insertions, 10 deletions

diff --git a/services/automerge/automerge.go b/services/automerge/automerge.go
index 9946047640..f001a6ccc5 100644
--- a/services/automerge/automerge.go
+++ b/services/automerge/automerge.go
@@ -25,11 +25,11 @@ import (
 )
 
 // prAutoMergeQueue represents a queue to handle update pull request tests
-var prAutoMergeQueue queue.UniqueQueue
+var prAutoMergeQueue *queue.WorkerPoolQueue[string]
 
 // Init runs the task queue to that handles auto merges
 func Init() error {
-	prAutoMergeQueue = queue.CreateUniqueQueue("pr_auto_merge", handle, "")
+	prAutoMergeQueue = queue.CreateUniqueQueue("pr_auto_merge", handler)
 	if prAutoMergeQueue == nil {
 		return fmt.Errorf("Unable to create pr_auto_merge Queue")
 	}
@@ -38,12 +38,12 @@ func Init() error {
 }
 
 // handle passed PR IDs and test the PRs
-func handle(data ...queue.Data) []queue.Data {
-	for _, d := range data {
+func handler(items ...string) []string {
+	for _, s := range items {
 		var id int64
 		var sha string
-		if _, err := fmt.Sscanf(d.(string), "%d_%s", &id, &sha); err != nil {
-			log.Error("could not parse data from pr_auto_merge queue (%v): %v", d, err)
+		if _, err := fmt.Sscanf(s, "%d_%s", &id, &sha); err != nil {
+			log.Error("could not parse data from pr_auto_merge queue (%v): %v", s, err)
 			continue
 		}
 		handlePull(id, sha)
@@ -52,10 +52,8 @@ func handle(data ...queue.Data) []queue.Data {
 }
 
 func addToQueue(pr *issues_model.PullRequest, sha string) {
-	if err := prAutoMergeQueue.PushFunc(fmt.Sprintf("%d_%s", pr.ID, sha), func() error {
-		log.Trace("Adding pullID: %d to the pull requests patch checking queue with sha %s", pr.ID, sha)
-		return nil
-	}); err != nil {
+	log.Trace("Adding pullID: %d to the pull requests patch checking queue with sha %s", pr.ID, sha)
+	if err := prAutoMergeQueue.Push(fmt.Sprintf("%d_%s", pr.ID, sha)); err != nil {
 		log.Error("Error adding pullID: %d to the pull requests patch checking queue %v", pr.ID, err)
 	}
 }