Form Builder - add an option to create a label (static text)

This could be used to either add arbitrary text to label another field (for instance, label a new signature field) or to essentially prefill data that cannot be altered by signers (for instance WBL coordinator phone number on a form were the coordinator doesn’t want to be a signer). In the latter example, this cannot currently be done because phone number is not a prefill option. Even if it were, we would not want another signer to be able to change it. It would also be beneficial if the values of these fields could be included in Form Data exports (if they are assigned a name).