Storage: validation and sanitization stubs (#50523)

* add `IsPathValidationError` util to fs api

* refactor storage.Upload method

* remove unused struct

* extract `RootUpload` constant

* move file validation outside of the service

* Make UploadErrorToStatusCode exported

* validation/sanitization

* refactor pathValidationError check

* refactor, rename sanitize to transform

* add a todo

* refactor

* transform -> sanitize

* lint fix

* #50608: fix jpg/jpeg

Co-authored-by: Tania B <yalyna.ts@gmail.com>
Co-authored-by: Ryan McKinley <ryantxu@gmail.com>

pkg/services/store/sanitize.go

@@ -0,0 +1,28 @@
+package store
+
+import (
+	"context"
+	"path/filepath"
+
+	"github.com/grafana/grafana/pkg/infra/filestorage"
+	"github.com/grafana/grafana/pkg/models"
+)
+
+func (s *standardStorageService) sanitizeUploadRequest(ctx context.Context, user *models.SignedInUser, req *UploadRequest, storagePath string) (*filestorage.UpsertFileCommand, error) {
+	if req.EntityType == EntityTypeImage {
+		ext := filepath.Ext(req.Path)
+		//nolint: staticcheck
+		if ext == ".svg" {
+			// TODO: sanitize svg
+		}
+	}
+
+	return &filestorage.UpsertFileCommand{
+		Path:               storagePath,
+		Contents:           req.Contents,
+		MimeType:           req.MimeType,
+		CacheControl:       req.CacheControl,
+		ContentDisposition: req.ContentDisposition,
+		Properties:         req.Properties,
+	}, nil
+}