Geo Documentation: Add Container Repositories as a documented Data Type

Why are we doing this work

Geo has thorough documentation regarding the supported Data Types and what they are. However, currently Container Repositories is not included in the documentation but is a supported Data Type in the application and represented in our UI. We should document it with the existing documentation.

Relevant links

• Data Type Docs: https://docs.gitlab.com/ee/administration/geo/replication/datatypes.html#data-types
• Follow up from conversation: #367087 (comment 2318872159)

Implementation plan

1. Add documentation to https://gitlab.com/gitlab-org/gitlab/-/blob/master/doc/administration/geo/replication/datatypes.md following a similar pattern to the existing Data Types in that file.