Reducing the filestore dependencies from the rest of the source code (#16816)

* Reducing the filestore dependencies from the rest of the source code

* Making more generic config conversion to FileBackendSettings

* Fixing usage of the NewFileBackend function

* Fixing more usages of the NewFileBackend function

* Fix some linter errors

* Fix more linter errors

* Fixing some unit tests

* Fixing linter problem

* Addressing PR review comments

* Simplifing the CopyFile for tests

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

api4/plugin_test.go

@@ -25,7 +25,6 @@ import (
 	"github.com/mattermost/mattermost-server/v5/model"
 	"github.com/mattermost/mattermost-server/v5/plugin"
 	"github.com/mattermost/mattermost-server/v5/testlib"
-	"github.com/mattermost/mattermost-server/v5/utils"
 	"github.com/mattermost/mattermost-server/v5/utils/fileutils"
 )
 
@@ -1552,9 +1551,9 @@ func TestInstallMarketplacePlugin(t *testing.T) {
 		prepackagedPluginsDir, found := fileutils.FindDir(prepackagedPluginsDir)
 		require.True(t, found, "failed to find prepackaged plugins directory")
 
-		err = utils.CopyFile(filepath.Join(path, "testplugin.tar.gz"), filepath.Join(prepackagedPluginsDir, "testplugin.tar.gz"))
+		err = testlib.CopyFile(filepath.Join(path, "testplugin.tar.gz"), filepath.Join(prepackagedPluginsDir, "testplugin.tar.gz"))
 		require.NoError(t, err)
-		err = utils.CopyFile(filepath.Join(path, "testplugin.tar.gz.asc"), filepath.Join(prepackagedPluginsDir, "testplugin.tar.gz.sig"))
+		err = testlib.CopyFile(filepath.Join(path, "testplugin.tar.gz.asc"), filepath.Join(prepackagedPluginsDir, "testplugin.tar.gz.sig"))
 		require.NoError(t, err)
 
 		th2 := SetupConfig(t, func(cfg *model.Config) {
@@ -1687,7 +1686,7 @@ func TestInstallMarketplacePlugin(t *testing.T) {
 		prepackagedPluginsDir, found := fileutils.FindDir(prepackagedPluginsDir)
 		require.True(t, found, "failed to find prepackaged plugins directory")
 
-		err = utils.CopyFile(filepath.Join(path, "testplugin.tar.gz"), filepath.Join(prepackagedPluginsDir, "testplugin.tar.gz"))
+		err = testlib.CopyFile(filepath.Join(path, "testplugin.tar.gz"), filepath.Join(prepackagedPluginsDir, "testplugin.tar.gz"))
 		require.NoError(t, err)
 
 		th := SetupConfig(t, func(cfg *model.Config) {