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)

tests/integration/api_branch_test.go

@@ -143,7 +143,6 @@ func testAPICreateBranches(t *testing.T, giteaURL *url.URL) {
 		},
 	}
 	for _, test := range testCases {
-		defer tests.ResetFixtures(t)
 		session := ctx.Session
 		testAPICreateBranch(t, session, "user2", "my-noo-repo", test.OldBranch, test.NewBranch, test.ExpectedHTTPStatus)
 	}

tests/integration/integration_test.go

@@ -29,6 +29,7 @@ import (
 	"code.gitea.io/gitea/modules/json"
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/setting"
+	"code.gitea.io/gitea/modules/testlogger"
 	"code.gitea.io/gitea/modules/util"
 	"code.gitea.io/gitea/modules/web"
 	"code.gitea.io/gitea/routers"
@@ -91,21 +92,21 @@ func TestMain(m *testing.M) {
 	// integration test settings...
 	if setting.CfgProvider != nil {
 		testingCfg := setting.CfgProvider.Section("integration-tests")
-		tests.SlowTest = testingCfg.Key("SLOW_TEST").MustDuration(tests.SlowTest)
-		tests.SlowFlush = testingCfg.Key("SLOW_FLUSH").MustDuration(tests.SlowFlush)
+		testlogger.SlowTest = testingCfg.Key("SLOW_TEST").MustDuration(testlogger.SlowTest)
+		testlogger.SlowFlush = testingCfg.Key("SLOW_FLUSH").MustDuration(testlogger.SlowFlush)
 	}
 
 	if os.Getenv("GITEA_SLOW_TEST_TIME") != "" {
 		duration, err := time.ParseDuration(os.Getenv("GITEA_SLOW_TEST_TIME"))
 		if err == nil {
-			tests.SlowTest = duration
+			testlogger.SlowTest = duration
 		}
 	}
 
 	if os.Getenv("GITEA_SLOW_FLUSH_TIME") != "" {
 		duration, err := time.ParseDuration(os.Getenv("GITEA_SLOW_FLUSH_TIME"))
 		if err == nil {
-			tests.SlowFlush = duration
+			testlogger.SlowFlush = duration
 		}
 	}
 
@@ -130,7 +131,7 @@ func TestMain(m *testing.M) {
 	// Instead, "No tests were found",  last nonsense log is "According to the configuration, subsequent logs will not be printed to the console"
 	exitCode := m.Run()
 
-	tests.WriterCloser.Reset()
+	testlogger.WriterCloser.Reset()
 
 	if err = util.RemoveAll(setting.Indexer.IssuePath); err != nil {
 		fmt.Printf("util.RemoveAll: %v\n", err)