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)

modules/queue/base_redis_test.go

@@ -0,0 +1,71 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package queue
+
+import (
+	"context"
+	"os"
+	"os/exec"
+	"testing"
+	"time"
+
+	"code.gitea.io/gitea/modules/nosql"
+	"code.gitea.io/gitea/modules/setting"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func waitRedisReady(conn string, dur time.Duration) (ready bool) {
+	ctxTimed, cancel := context.WithTimeout(context.Background(), time.Second*5)
+	defer cancel()
+	for t := time.Now(); ; time.Sleep(50 * time.Millisecond) {
+		ret := nosql.GetManager().GetRedisClient(conn).Ping(ctxTimed)
+		if ret.Err() == nil {
+			return true
+		}
+		if time.Since(t) > dur {
+			return false
+		}
+	}
+}
+
+func redisServerCmd(t *testing.T) *exec.Cmd {
+	redisServerProg, err := exec.LookPath("redis-server")
+	if err != nil {
+		return nil
+	}
+	c := &exec.Cmd{
+		Path:   redisServerProg,
+		Args:   []string{redisServerProg, "--bind", "127.0.0.1", "--port", "6379"},
+		Dir:    t.TempDir(),
+		Stdin:  os.Stdin,
+		Stdout: os.Stdout,
+		Stderr: os.Stderr,
+	}
+	return c
+}
+
+func TestBaseRedis(t *testing.T) {
+	var redisServer *exec.Cmd
+	defer func() {
+		if redisServer != nil {
+			_ = redisServer.Process.Signal(os.Interrupt)
+			_ = redisServer.Wait()
+		}
+	}()
+	if !waitRedisReady("redis://127.0.0.1:6379/0", 0) {
+		redisServer = redisServerCmd(t)
+		if redisServer == nil && os.Getenv("CI") != "" {
+			t.Skip("redis-server not found")
+			return
+		}
+		assert.NoError(t, redisServer.Start())
+		if !assert.True(t, waitRedisReady("redis://127.0.0.1:6379/0", 5*time.Second), "start redis-server") {
+			return
+		}
+	}
+
+	testQueueBasic(t, newBaseRedisSimple, toBaseConfig("baseRedis", setting.QueueSettings{Length: 10}), false)
+	testQueueBasic(t, newBaseRedisUnique, toBaseConfig("baseRedisUnique", setting.QueueSettings{Length: 10}), true)
+}