Resolve "User activity is stuck loading when there is none"

What does this MR do?

Hides the loading spinner and displays a message (No activities found) on the user profile overview when there are no activities yet.

It also adds the message No activities found to the Activity dashboard and to the Activity tab (on the user profile page) when there are no activities to be consistent with other views.

Screenshots:

page	before	after
User profile overview
User profile activity
Activity dashboard

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/55755

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Tested in all supported browsers
• 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

Closes #55755 (closed)