Disable Webform Submit Button on Form Submit

[kevincrafts]

We're seeing a rise in tickets where a web form is getting multiple submissions all at once, possibly by the user clicking the submit button multiple times. To prevent this from happening, we can disable the submit button when the form has been submitted, preventing multiple clicks if there is any sort of delay.

This action should be taken with the form submit handler vs onclick because it will allow validation to process which would happen before form submit, vs afterwards of a onclick which would then make it impossible to submit the form.