API to configure SAML Group Links
### Proposal GitLab supports provisioning access to the groups (or subgroups) via [SAML Group Links](https://docs.gitlab.com/ee/user/group/saml_sso/#group-sync). At this time, I was not able to find an API how to configure it in the REST API documentation. UC: As an "owner" of the gitlab group, I would like to manage groups and subgroups automatic membership (via SAML Group Links) by the "Infrastructure-as-Code", specifically terraform.
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