Nav changes: Review & update "Manage Elastic Defend" and "Endpoint response actions" sections

[joepeeples]

Sub-issue of #5896.

Priority is to update stateful/ESS, but should try to align serverless with any updates as well.

### Tasks
- [x] [Manage Elastic Defend](https://www.elastic.co/guide/en/security/current/sec-manage-intro.html)
- [x] [Endpoint response actions](https://www.elastic.co/guide/en/security/current/response-actions.html)