[REST Source] completes renaming of default_paginator to paginator

[willi-mueller]

Tell us what you do here

• [x] fixing a bug (please link a relevant bug report)

Relevant issue

issue #313

More PR info

I forgot to commit this file in https://github.com/dlt-hub/verified-sources/pull/367. This PR completes that refactoring.

[burnash]

Cheers!