[11.11] Add support for additional parameters in Projects::forks

[fjgarlin]

The forks endpoint allows a handy search parameter, so define it as an option.

See the options for forks endpoint: https://docs.gitlab.com/ee/api/projects.html#list-forks-of-a-project

With the following code:

      $forks = $gitlab_client->projects()->forks($project, [
        'search' => 'search_term',
      ]);

Currently: throws exception as parameter is not defined.
After applying changes: returns list of forks that match "search_term"

[GrahamCampbell]

Thanks for the PR. Please address the inline comments and add test coverage.

[fjgarlin]

Inline comments were addressed and test coverage was added. Pleae review.

[GrahamCampbell]

Thanks.