Use DA /put path from spec (ethereum-optimism#12081)

* Accept /put path as described in spec

In addition to the currently used `/put/` path to ease the migration.
See ethereum-optimism#11499.

* 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
 }

op-alt-da/daserver.go

@@ -54,6 +54,7 @@ func (d *DAServer) Start() error {
 
 	mux.HandleFunc("/get/", d.HandleGet)
 	mux.HandleFunc("/put/", d.HandlePut)
+	mux.HandleFunc("/put", d.HandlePut)
 
 	d.httpServer.Handler = mux
 
@@ -128,7 +129,7 @@ func (d *DAServer) HandlePut(w http.ResponseWriter, r *http.Request) {
 	d.log.Info("PUT", "url", r.URL)
 
 	route := path.Dir(r.URL.Path)
-	if route != "/put" {
+	if route != "/put" && r.URL.Path != "/put" {
 		w.WriteHeader(http.StatusBadRequest)
 		return
 	}