Hide confidential events in ruby

What does this MR do?

This hides events the current_user does not have access to by filtering them out in the EventsFinder. That finder now returns a paginatable array. The pagination itself is also done in the finder to limit the amount of events loaded into memory.

The FinderWithCrossProjectAccess was not yet compatible with array's returned from the execute method, so I've added the option to define the model to be returned

What are the relevant issue numbers?

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/51791

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• Security reports checked/validated by reviewer