Split BaseService to ContainerBaseService

What does this MR do?

Currently BaseService accepts a project. However we need to expand it to accept either a group or a project, since wiki can now belong to group. This MR introduces a ContainerBaseService, where the container can either be a project or a group.

The original BaseService will be more barebone, not knowing projects at all. This opens up future improvement opportunities for some service classes since they aren't really related to project at all.

One main discussion is on the naming choice of ContainerBaseService. If you want to discuss about this, join the thread here: !30681 (comment 333725944)

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.