Decouple group and project level merge request approval settings

The GitLab API docs for merge request approval settings made it seem like selective_code_owner_removals was available at group and project level. See the discussion here: gitlab-org/terraform-provider-gitlab!2588 (comment 2688878372)

In order to remove selective_code_owner_removals as a option for the group endpoints, we will need to have a different struct for UpdateMergeRequestApprovalSettingsOptions .

This would be a breaking change so would be in the 1.0 milestone.

Implementation Guide

• Rename UpdateMergeRequestApprovalSettingsOptions to UpdateProjectMergeRequestApprovalSettingsOptions.
• Create a copy of UpdateProjectMergeRequestApprovalSettingsOptions called UpdateGroupRequestApprovalSettingsOptions but without the SelectiveCodeOwnerRemovals field.
• Update UpdateGroupMergeRequestApprovalSettings to use UpdateGroupRequestApprovalSettingsOptions.
• Update UpdateProjectMergeRequestApprovalSettings to use UpdateProjectMergeRequestApprovalSettingsOptions.
• Update remaining test and interface references to use the new struct names.