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>

app/file.go

@@ -80,7 +80,8 @@ func (a *App) FileBackend() (filesstore.FileBackend, *model.AppError) {
 }
 
 func (a *App) CheckMandatoryS3Fields(settings *model.FileSettings) *model.AppError {
-	err := filesstore.CheckMandatoryS3Fields(settings)
+	fileBackendSettings := settings.ToFileBackendSettings(false)
+	err := fileBackendSettings.CheckMandatoryS3Fields()
 	if err != nil {
 		return model.NewAppError("CheckMandatoryS3Fields", "api.admin.test_s3.missing_s3_bucket", nil, err.Error(), http.StatusBadRequest)
 	}
@@ -101,7 +102,7 @@ func (a *App) TestFilesStoreConnection() *model.AppError {
 
 func (a *App) TestFilesStoreConnectionWithConfig(cfg *model.FileSettings) *model.AppError {
 	license := a.Srv().License()
-	backend, err := filesstore.NewFileBackend(cfg, license != nil && *license.Features.Compliance)
+	backend, err := filesstore.NewFileBackend(cfg.ToFileBackendSettings(license != nil && *license.Features.Compliance))
 	if err != nil {
 		return model.NewAppError("FileBackend", "api.file.no_driver.app_error", nil, err.Error(), http.StatusInternalServerError)
 	}