fix: [Rules > Add Elastic rules][SCREEN READER]: Rule non-modal flyou…

…t must announce itself on render and manage focus (#181427)

Closes: elastic/security-team#8657

## Summary

The part about announcing the title was fixed in that PR:
#180888. This PR removed the
incorrect 'ownFocus = { false }' parameter for `EuiFlyout`. Since that
flyout overlaps the table, we should not open it with that option.

### Screen 


![image](https://github.com/elastic/kibana/assets/20072247/50883abb-7a76-4819-8df4-530c81d1a48c)

#### Eui documentation
https://eui.elastic.co/#/layout/flyout#without-ownfocus

x-pack/plugins/security_solution/public/detection_engine/rule_management/components/rule_details/rule_details_flyout.tsx

@@ -191,11 +191,11 @@ export const RuleDetailsFlyout = ({
       id={id}
       size={size}
       onClose={closeFlyout}
-      ownFocus={false}
       key="prebuilt-rules-flyout"
       paddingSize="l"
       data-test-subj={dataTestSubj}
       aria-labelledby={prebuiltRulesFlyoutTitleId}
+      ownFocus
     >
       <EuiFlyoutHeader>
         <EuiTitle size="m">