feat(user): allow renaming security keys (webauthn/passkey) (#39413)

Closes https://github.com/go-gitea/gitea/issues/39287

Security key nicknames could only be set at registration, so a skipped
nickname left an auto-generated hex name until the key was
re-registered. Each key now has a Rename button opening a dialog with
the current nickname. A nickname used by another of the user's keys
(case-insensitive) or a blank nickname is rejected. Renames are recorded
as `user:webauth:rename` audit events.

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

services/forms/user_form.go

@@ -287,7 +287,14 @@ type TwoFactorScratchAuthForm struct {
 // WebauthnRegistrationForm for reserving an WebAuthn name
 type WebauthnRegistrationForm struct {
 	middleware.FormDefaultValidator
-	Name string `binding:"Required"`
+	Name string `binding:"TrimSpace;MaxSize(255)"`
+}
+
+// WebauthnRenameForm for renaming a WebAuthn credential
+type WebauthnRenameForm struct {
+	middleware.FormDefaultValidator
+	ID   int64  `binding:"Required"`
+	Name string `binding:"TrimSpace;Required;MaxSize(255)"`
 }
 
 // PackageSettingForm form for package settings