Add missing parameters and endpoint support available only to Ultimate instances

[Rein142]

Description

Hello, while skimming through the codebase, I noticed that certain endpoints and parameters which are only available to Ultimate GitLab instances are not supported, I wondered if this could be added.

An example of an endpoint which is only available for Ultimate is https://gitlab.com/api/v4/groups/:id/related_epic_links.

An example of a Project parameter only available to Ultimate is only_allow_merge_if_all_status_checks_passed.

Proposal

Add support to these endpoints and parameters so that interaction can be made available through Gitbeaker. To check what parameters and endpoints these are, I went to https://docs.gitlab.com/ee/api/groups.html and https://docs.gitlab.com/ee/api/projects.html. Within the pages I searched for . Ultimate only to easily find the ones only available to Ultimate.

Checklist

• I have checked that this is not a duplicate issue.
• I have read the documentation.

[Rein142]

To add to this request. Custom roles are also a thing in Ultimate, the API handles this by adding a member_role object which includes the name, base access level and permissions that this role has, is there a chance custom roles will be supported by Gitbeaker as well in the future?