Add pagination in api-gateway

[Shahar-Y]

Allow pagination with two query params:

• pageNum
• pageSize

If both are received and are non-negative, return the relevant page.

This should include the three options in the epic:

• [x] Files shared with me: meateam/permission-service#10
• [ ] Get files by folder.
• [ ] Get my files (root fiolder).

[Shahar-Y]

Closed in #199