Mono repo -> Master (#22553)

Combines the following repositories into one:

https://github.com/mattermost/mattermost-server
https://github.com/mattermost/mattermost-webapp
https://github.com/mattermost/focalboard
https://github.com/mattermost/mattermost-plugin-playbooks

server/channels/app/plugin_shutdown_test.go

@@ -0,0 +1,74 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package app
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestPluginShutdownTest(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping test to verify forced shutdown of slow plugin")
+	}
+
+	th := Setup(t)
+	defer th.TearDown()
+
+	tearDown, _, _ := SetAppEnvironmentWithPlugins(t,
+		[]string{
+			`
+			package main
+
+			import (
+				"github.com/mattermost/mattermost-server/v6/plugin"
+			)
+
+			type MyPlugin struct {
+				plugin.MattermostPlugin
+			}
+
+			func main() {
+				plugin.ClientMain(&MyPlugin{})
+			}
+			`,
+			`
+			package main
+
+			import (
+				"github.com/mattermost/mattermost-server/v6/plugin"
+			)
+
+			type MyPlugin struct {
+				plugin.MattermostPlugin
+			}
+
+			func (p *MyPlugin) OnDeactivate() error {
+				c := make(chan bool)
+				<-c
+
+				return nil
+			}
+
+			func main() {
+				plugin.ClientMain(&MyPlugin{})
+			}
+		`,
+		}, th.App, th.NewPluginAPI)
+	defer tearDown()
+
+	done := make(chan bool)
+	go func() {
+		defer close(done)
+		th.App.ch.ShutDownPlugins()
+	}()
+
+	select {
+	case <-done:
+	case <-time.After(15 * time.Second):
+		require.Fail(t, "failed to force plugin shutdown after 10 seconds")
+	}
+}