[Internal]: [SECURITY SOLUTION | EDR] Document the availability of `kill-process --kill-descendants` featrure

### Description

New feature that adds the option to terminate descendant processes when killing a process. A new arguments - `--kill-descendants` - was added to the existing `kill-process` response action

This feature will be release with `v9.6.0`, including making it available in serverless right around the same time this release goes GA

### Resources

Epic can be found here: https://github.com/elastic/security-team/issues/15486

### Which deployment methods does this change impact?

Elastic On-Prem and Cloud (all)

### Feature differences

Identical in all deployments.

### What Elastic Stack release is this request related to?

9.6

### Serverless release

Week of October 21 (same as GA for 9.6)

### Collaboration model

The documentation team will create the first draft

### Point of contact.

**Main contact:**

- @paul-tavares

**Stakeholders:**

- @raqueltabuyo / @roxana-gheorghe
- @intxgo
- @paul-tavares