Implement client for default permission endpoints

[kushagra189]

Currently, we have kept the default permission endpoints as fixed paths. Instead, we should probably focus on adding a client for the default API, and for that, we know the routes. Users might still be able to reuse that client if they host a /permissions API at the expected base path (if all they are doing is modifying the behavior of the default endpoints). And if they wanna add a completely different API, then they would also need to implement the client along with it.
Hence, we need to implement a client for the default permission endpoints, which then can be used in the controller logic of a FOCA app.

[uniqueg]

Just to note that the default client should be passed the base path of course, i.e., everything before /permissions

[kushagra189]

#157