[MM-28422] Enable processing of import files through API (#16062)

* Implement unzip function

* Implement FileSize method

* Implement path rewriting for bulk import

* Small improvements

* Add ImportSettings to config

* Implement ListImports API endpoint

* Enable uploading import files

* Implement import process job

* Add missing license headers

* Address reviews

* Make path sanitization a bit smarter

* Clean path before calculating Dir

* [MM-30008] Add mmctl support for file imports (#16301)

* Add mmctl support for import files

* Improve test

* Remove unnecessary handlers

* Use th.TestForSystemAdminAndLocal

* Make nouser id a constant

app/file.go

@@ -101,6 +101,14 @@ func (a *App) FileExists(path string) (bool, *model.AppError) {
 	return backend.FileExists(path)
 }
 
+func (a *App) FileSize(path string) (int64, *model.AppError) {
+	backend, err := a.FileBackend()
+	if err != nil {
+		return 0, err
+	}
+	return backend.FileSize(path)
+}
+
 func (a *App) MoveFile(oldPath, newPath string) *model.AppError {
 	backend, err := a.FileBackend()
 	if err != nil {