goimports (#16640)

* format using `goimports -local github.com/mattermost/mattermost-server/v5 -w`

* added goimports lint check to .golangci.yml

* format using `goimports -local github.com/mattermost/mattermost-server/v5 -w` for a corner case

* make app-layers, *-mocks and store-layers for ci check

Co-authored-by: Mahmudul Haque <mahmudulhaque@protonmail.com>
Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

app/plugin_api_tests/manual.test_http_upgrade_websocket_plugin/main.go

@@ -7,10 +7,10 @@ import (
 	"bytes"
 	"net/http"
 
+	"github.com/gorilla/websocket"
+
 	"github.com/mattermost/mattermost-server/v5/model"
 	"github.com/mattermost/mattermost-server/v5/plugin"
-
-	"github.com/gorilla/websocket"
 )
 
 type Plugin struct {

app/plugin_api_tests/test_call_log_api_plugin/main.go

@@ -4,9 +4,10 @@
 package main
 
 import (
+	"github.com/pkg/errors"
+
 	"github.com/mattermost/mattermost-server/v5/model"
 	"github.com/mattermost/mattermost-server/v5/plugin"
-	"github.com/pkg/errors"
 )
 
 type PluginUsingLogAPI struct {