feat: implement 'rewrite' storage middleware

This allows to rewrite 'URLFor' of the storage driver to use a specific
host/trim the base path.

It is different from the 'redirect' middleware, as it still calls the
storage driver URLFor.

For example, with Azure storage provider, this allows to transform the
SAS Azure Blob Storage URL into the URL compatible with Azure Front
Door.

Signed-off-by: Andrey Smirnov <andrey.smirnov@siderolabs.com>

registry/storage/driver/middleware/rewrite/middleware_test.go

@@ -0,0 +1,75 @@
+package middleware
+
+import (
+	"context"
+	"net/http"
+	"testing"
+
+	"github.com/distribution/distribution/v3/registry/storage/driver/base"
+	"github.com/stretchr/testify/require"
+)
+
+type mockSD struct {
+	base.Base
+}
+
+func (*mockSD) RedirectURL(_ *http.Request, urlPath string) (string, error) {
+	return "http://some.host/some/path/file", nil
+}
+
+func TestNoConfig(t *testing.T) {
+	options := make(map[string]interface{})
+	middleware, err := newRewriteStorageMiddleware(context.Background(), &mockSD{}, options)
+	require.NoError(t, err)
+
+	_, ok := middleware.(*rewriteStorageMiddleware)
+	require.True(t, ok)
+
+	url, err := middleware.RedirectURL(nil, "")
+	require.NoError(t, err)
+	require.Equal(t, "http://some.host/some/path/file", url)
+}
+
+func TestWrongType(t *testing.T) {
+	options := map[string]interface{}{
+		"scheme": 1,
+	}
+	_, err := newRewriteStorageMiddleware(context.TODO(), nil, options)
+	require.ErrorContains(t, err, "scheme must be a string")
+}
+
+func TestRewriteHostsScheme(t *testing.T) {
+	options := map[string]interface{}{
+		"scheme": "https",
+		"host":   "example.com",
+	}
+
+	middleware, err := newRewriteStorageMiddleware(context.TODO(), &mockSD{}, options)
+	require.NoError(t, err)
+
+	m, ok := middleware.(*rewriteStorageMiddleware)
+	require.True(t, ok)
+	require.Equal(t, "https", m.overrideScheme)
+	require.Equal(t, "example.com", m.overrideHost)
+
+	url, err := middleware.RedirectURL(nil, "")
+	require.NoError(t, err)
+	require.Equal(t, "https://example.com/some/path/file", url)
+}
+
+func TestTrimPrefix(t *testing.T) {
+	options := map[string]interface{}{
+		"trimpathprefix": "/some/path",
+	}
+
+	middleware, err := newRewriteStorageMiddleware(context.TODO(), &mockSD{}, options)
+	require.NoError(t, err)
+
+	m, ok := middleware.(*rewriteStorageMiddleware)
+	require.True(t, ok)
+	require.Equal(t, "/some/path", m.trimPathPrefix)
+
+	url, err := middleware.RedirectURL(nil, "")
+	require.NoError(t, err)
+	require.Equal(t, "http://some.host/file", url)
+}