Refactor project_or_wiki to container

What does this MR do?

project_or_wiki is a variable name used in EE's Geo module, for computing the repository paths. It is less applicable now since snippets will also contain a repository.

By renaming it as container we can remove many redundant code.

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.