Add loading state and remove custom button position.

Based on PR feedback https://github.com/mailpoet/mailpoet/pull/5972#issuecomment-2516596159, The Email editor cannot work without a template. So, we currently don't need to set up workflow to support template not loading

MAILPOET-6331

packages/js/email-editor/src/components/template-select/select-modal.tsx

@@ -120,13 +120,12 @@ export function SelectTemplateModal( { onSelectCallback } ) {
 						) ) }
 					</div>
 
-					<Flex justify={ hasTemplates ? 'flex-end' : 'center' }>
+					<Flex justify="flex-end">
 						<FlexItem>
 							<Button
-								variant={
+								variant="tertiary"
-									hasTemplates ? 'tertiary' : 'primary'
-								}
 								onClick={ () => handleCloseWithoutSelection() }
+								isBusy={ ! hasTemplates }
 							>
 								{ __( 'Start from scratch', 'mailpoet' ) }
 							</Button>