[IMP] website_form: keep label when input changes

Changing the input type should not change the label name.

The goal of this commit is to keep old label when input type
changes and set the default label names for new fields only.

Part of https://github.com/odoo/odoo/pull/68061
task-2431484

addons/website_form/static/src/snippets/s_website_form/options.js

@@ -821,8 +821,8 @@ options.registry.WebsiteFieldEditor = FieldEditor.extend({
         if (!value) {
             return;
         }
-        const name = this.el.querySelector(`[data-custom-field="${value}"]`).textContent;
-        const field = this._getCustomField(value, `Custom ${name}`);
+        const oldLabelText = this.$target[0].querySelector('.s_website_form_label_content').textContent;
+        const field = this._getCustomField(value, oldLabelText);
         this._setActiveProperties(field);
         await this._replaceField(field);
         this.rerender = true;