[docs-patrol] Update AWS CloudTrail docs for host/entity target classification change

Recent code changes in the repository have introduced documentation drift. The following change needs a corresponding documentation update.

## Changes Requiring Documentation Updates

### 1. CloudTrail target entity routing changed, but exported-fields docs still describe old behavior

**Commit(s):** [`7d3b60b1ce81caf1121f360d71717179d8fff521`](https://github.com/elastic/integrations/commit/7d3b60b1ce81caf1121f360d71717179d8fff521)

**What changed:**
- In `packages/aws/data_stream/cloudtrail/elasticsearch/ingest_pipeline/default.yml`, host classification now only treats EC2 instances as host targets:
- `hostResourceTypes` now only includes `instance` (lines 72-74).
- `hostIdPrefixes` now only includes `i-` (lines 112-114).
- Non-host targets now flow to generic target storage (`entity.target.id`) (lines 926-945).
- `host.id` is now set when host targets are present (lines 936-939).

**Documentation impact:**
- `packages/aws/docs/cloudtrail.md` still states that `host.target.entity.id` includes EBS volume, snapshot, and AMI IDs (line 142), which no longer matches ingest behavior.
- The same exported-fields table does not document `host.id`.

This is concretely user-impacting: queries or detections built from docs will look for snapshot/AMI/volume identifiers in `host.target.entity.id`, but those identifiers are now emitted under `entity.target.id`.

## Suggested Actions

- [ ] Update `packages/aws/docs/cloudtrail.md` exported-fields entry for `host.target.entity.id` to reflect EC2-instance-only host target classification.
- [ ] Add exported-fields documentation for `host.id` in `packages/aws/docs/cloudtrail.md`.
- [ ] Regenerate/update built docs under `packages/aws/_dev/build/docs/cloudtrail.md` to stay aligned.

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