[11.14] Group milestones API: able to call GitLab API with addtional parameters updated_before and updated_after

[wenchaoxue]

List group milestones new parameters

updated_before:
Return only milestones updated before the given datetime. Expected in ISO 8601 format (2019-03-15T08:00:00Z).
Introduced in GitLab 15.10

updated_after:
Return only milestones updated after the given datetime. Expected in ISO 8601 format (2019-03-15T08:00:00Z).
Introduced in GitLab 15.10

• call Group milestones API with addtional parameters updated_before and updated_after and add unit tests
• add missing unit tests on the parameters iids, state, search

[GrahamCampbell]

Thanks.