MM-19553: Generate valid passwords on bulk import. (#12871)

This changes the bulk import so when it needs to generate a password
because no password or auth data was supplied, it now takes into account
the configured minimum length, as well as assuming all other distinct
character types are configured to be required. It should now generate
valid passwords regardless of the password policy configuration in the
Mattermost configuration file.

app/import_functions.go

@@ -334,7 +334,7 @@ func (a *App) ImportUser(data *UserImportData, dryRun bool) *model.AppError {
 		authData = nil
 	} else {
 		// If no AuthData or Password is specified, we must generate a password.
-		password = model.NewId()
+		password = model.GeneratePassword(*a.Config().PasswordSettings.MinimumLength)
 		authData = nil
 	}