Option to deactivate the client portal

What version of Invoice Ninja are you running? ie v4.5 / v5 v4.5.31 What environment are you running? Self-Hosting Have you searched existing issues/requests? Yes Additional context First of all: great work, I love the program so far and hope to join development soon. One quick "feature" I would like to see would be the deactivation of the Client Portal. Why? It is a good idea, sadly none of my clients wants to use, but I see a huge misuse potential, as my invoices are still accessible without authentication and authorization. This is a security concern for me, as from the invoices one can read personal information about me and my clients. I know that the chances are slim that anyone actually crawls for or guesses the link, but if one would the damage would be significant. My workaround is to set a password for every client, even tho they won't use it, just so that the invoices are hidden. My suggestion would be that the checkbox for "Client Portal&…