Propagate ETag from gitea (#93)

close #15

Co-authored-by: 6543 <6543@obermui.de>
Reviewed-on: https://codeberg.org/Codeberg/pages-server/pulls/93

server/gitea/client.go

@@ -25,6 +25,7 @@ type Client struct {
 
 type FileResponse struct {
 	Exists   bool
+	ETag     []byte
 	MimeType string
 	Body     []byte
 }