Add new signature to Employee document

Add new signature Employee document. File could be signed by attached PNG (with real screenshot take) or by Text (you can use handwriting like font in UI for that).
Signature can be attached to any type of document.
Signature is database logged entity which can be read from system but doesn't change document anyway. So downloaded document will not contains signature in any form.
Database storing call parameters but also user who signed, IP address and time/date into entity.
This endpoint can be called by all user type. Employee will get list of his own documents only.\