Resolve "Endless scroll loader is visible on user profile overview page"

What does this MR do?

Adds a container property to the pager.js in order to enable scoping of the .loading selector. Otherwise the first matching page element will be selected which can lead to problems when multiple DOM elements with the same class appear on the site. (for example when switching tabs on the user's profile page)

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/53023

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

Closes #53023 (closed)