Adding a user to the platform let them accept if he/she agrees to join the platform

[emanuelaepure10]

Please follow the template below and provide at least information for
the first 4 sections

Background and Motivation

When adding a user to the platform we need to let them accept if he/ she agrees to join the platform , this would imply to changing the behavior and the content of the message below in two ways:
8a. parametrizing the sender information below, so that it take the value from the configuration of the system. ( taking the value of the registry manager could be an idea)
8b. Sending a first email allowing the user to accept the invitation to join the Re3gistry management platform ( as done for newsletters, for example) , that is needed from a GDPR point of view. If he accepts to join the platform then he can join the management interface
8b1. Connected to "8b", allow to make a self registration, classical button "Sign up", to be then accepted or nor by the Re3gistry manager