MM-16261: Synchronize plugins in HA (#11657)

* MM-16272 - Synchronize plugins across cluster (#11611)

* MM-16272 - Synchronize plugins across cluster

* Adding a test

* MM-16272 - Fixed tests

* MM-16272 - PR feedback

* MM-16270 - Plugin Sync (#11615)

* Initial implementation for plugin synch with file store. WIP

* Removed ListAll implementation. Used ListDirectory and change localstore to be consistent and return all items (files and folders) from directory

* Refactored plugin filestore operations out of main install/remove plugin

* Fixing error handling details

* Changes to use structured logging

* More logging fixes

* Wording and comments improvements

* Error handling and control flow improvements

* Changed managed flag check to use os.stat

* Added file store plugin dir and filename consts

* Replaced FileRead to use a the FileReader in PluginSync

* Minor styling and PR feedback changes

* Minor error handling improvements

* Added unit test for SyncPlugins. Changed SyncPlugins to use plugins environment to list available plugins

* PR Feedback improvements

* Minor err handling fix

* Removing FileStorePath from PluginEventData (#11644)

* Fix plugin path (#11654)

* tweak path, logging

Fix an issue not finding the plugins folder in S3. Tweak logging messages to add additional clarity.

* Removing FileExists check when Syncing plugins. Updated localstore to not return an error when directory does not exist

* PR Feedback

* Install prepackaged plugins locally only (#11656)

* s/uninstall/remove

* Updated ClusterMessage comment

* Updated PluginSync to test against s3 + local storage

model/plugin_event_data.go

@@ -0,0 +1,25 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package model
+
+import (
+	"encoding/json"
+	"io"
+)
+
+// PluginEventData used to notify peers about plugin changes.
+type PluginEventData struct {
+	Id string `json:"id"`
+}
+
+func (p *PluginEventData) ToJson() string {
+	b, _ := json.Marshal(p)
+	return string(b)
+}
+
+func PluginEventDataFromJson(data io.Reader) PluginEventData {
+	var m PluginEventData
+	json.NewDecoder(data).Decode(&m)
+	return m
+}