[UX] Use loading prompt for loading state of the feature screens

[xeniatup]

What is the bug?
When a page is loading it displays an empty prompt which is misleading for the users, especially if the wait time is significant.

How can one reproduce the bug?
Select any feature page from Security Analytics nav (Findings, Alerts, etc.), observe the empty prompt until the resulting table/graph is loaded.

What is the expected behavior?
The empty prompt should be used for the cases when no results are returned after the query is complete. For the loading state we can either show the loading prompt (probably the simplest solution) or a skeleton of the page with elements in loading state.

Do you have any screenshots?

loading-issue.mp4

[dblock]

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