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_requests.go

@@ -4,16 +4,16 @@
 package app
 
 import (
+	"bytes"
 	"fmt"
+	"io/ioutil"
 	"net/http"
 	"path"
 	"path/filepath"
 	"strings"
 
-	"bytes"
-	"io/ioutil"
-
 	"github.com/gorilla/mux"
+
 	"github.com/mattermost/mattermost-server/v5/mlog"
 	"github.com/mattermost/mattermost-server/v5/model"
 	"github.com/mattermost/mattermost-server/v5/plugin"