[GEN-2303]: fix loader for namespace-sources (#2371)

This pull request includes changes to the
`frontend/webapp/containers/main/sources/choose-sources/choose-sources-body/choose-sources-body-fast/sources-list/index.tsx`
file to improve the user experience by updating the styling and handling
the loading state for namespaces.

Styling improvements:
* Changed the `NoDataFoundWrapper` component's margin to padding for
better spacing and layout.

User experience improvements:
* Updated the `SourcesList` component to display a loading spinner
(`FadeLoader`) when namespaces are loading, instead of showing the "No
sources available" message.

frontend/webapp/containers/main/sources/choose-sources/choose-sources-body/choose-sources-body-fast/sources-list/index.tsx

@@ -60,7 +60,7 @@ const SelectionCount = styled(Text)`
 `;
 
 const NoDataFoundWrapper = styled.div`
-  margin: 50px 0;
+  padding: 50px 0;
   display: flex;
   flex-direction: column;
   align-items: center;
@@ -150,7 +150,7 @@ export const SourcesList: React.FC<Props> = ({
                 </RelativeWrapper>
               ) : (
                 <NoDataFoundWrapper>
-                  <NoDataFound title='No sources available in this namespace' subTitle='Try searching again or select another namespace.' />
+                  {namespacesLoading ? <FadeLoader scale={1.5} /> : <NoDataFound title='No sources available in this namespace' subTitle='Try searching again or select another namespace.' />}
                 </NoDataFoundWrapper>
               ))}
           </Group>