alt-DA: write to /put path as described in spec

The spec mandates using `/put` and not `/put/`, so that is what we
should do.

Warning: This will break DA solutions that only accept `/put/` at the
moment. It is recommended that DA solutions support both paths for a
while, so that updating OP-stack can happen independently of the exact
DA implementation version.

Closes ethereum-optimism#11499.

op-alt-da/daclient.go

@@ -119,7 +119,7 @@ func (c *DAClient) setInput(ctx context.Context, img []byte) (CommitmentData, er
 	}
 
 	body := bytes.NewReader(img)
-	url := fmt.Sprintf("%s/put/", c.url)
+	url := fmt.Sprintf("%s/put", c.url)
 	req, err := http.NewRequestWithContext(ctx, http.MethodPost, url, body)
 	if err != nil {
 		return nil, fmt.Errorf("failed to create HTTP request: %w", err)

op-alt-da/damock.go

@@ -141,7 +141,7 @@ func (s *FakeDAServer) Start() error {
 	// Override the HandleGet/Put method registrations
 	mux := http.NewServeMux()
 	mux.HandleFunc("/get/", s.HandleGet)
-	mux.HandleFunc("/put/", s.HandlePut)
+	mux.HandleFunc("/put", s.HandlePut)
 	s.httpServer.Handler = mux
 	return nil
 }