Add KB on how to work around the "An invalid form control with name='x' is not focusable" issue

[petar-i-todorov]

There is a bug where "Send Email" inputs are included in the HTML even if the "Send Email" functionality is disabled. This causes issues in WebForms (and not only) environments that rely on <form> elements. If the viewer with these hidden inputs is rendered inside of a form, and a button inside the form triggers a form submission, an error will occur in the browser stating that there are invalid form inputs that are not focusable.

The workaround is to use a custom template to remove these inputs from the HTML content of the viewer.

Consider adding a KB on this topic, which can be referenced in the future even after the bug is fixed.