Custom links in the client portal

What version of Invoice Ninja are you running? ie v4.5 / v5
v5

What environment are you running?
Docker

Have you searched existing issues/requests?
Yes

Additional context
I would love to get the option to add external links to the client portal, probably depending on subscribed services.
(But both should be possible: General and subscription based)

Thinking of something like this:
![image](