Add a global page size variable for the Agent-based SCA client

[Gby56]

Hi @tjarrettveracode !

I'm having a bug currently with the SourceClear API, and the only fix would be to set the pagination size to a bigger one. Its on the get_projects() function, but it got me thinking, looking at the apihelper.py, the _rest_paged_request() function could maybe inject a page size param, with a setting in the client constructor ?

I'll make a PR to show what I'm thinking about, it would really help