[docs-patrol] Document new `queue.slab` internal queue type in Beat queue docs

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

## Changes Requiring Documentation Updates

### 1. New `queue.slab` queue type is available but not documented in internal-queue docs

**Commit(s):**
- 37398496f55a6e1f7f75869e6f21144f0430dd21 ([link](https://github.com/elastic/beats/commit/37398496f55a6e1f7f75869e6f21144f0430dd21))

**What changed:**
- `libbeat/publisher/queue/slabqueue/slabqueue.go:19` states: "both by standalone Beats (selectable via queue.slab)"
- `libbeat/publisher/queue/slabqueue/slabqueue.go:56` states: "from a pipeline config (queue.slab) just like the other implementations."
- `libbeat/publisher/queue/slabqueue/slabqueue.go:57` defines `const QueueType = "slab"`
- `libbeat/publisher/pipeline/pipeline.go:374` adds `case slabqueue.QueueType:` for queue factory selection
- `libbeat/tests/system/config/libbeat.yml.j2:57` contains `queue.slab:` test config path

**Documentation impact:**
- Current internal queue docs list/examples only `queue.mem` and `queue.disk` (for example `docs/reference/filebeat/configuring-internal-queue.md:20` and `:86`) and do not mention `queue.slab`.
- Update internal queue docs to include `queue.slab` as a supported type, with usage and key behavior notes.
- Affected docs pages:
- `docs/reference/filebeat/configuring-internal-queue.md`
- `docs/reference/metricbeat/configuring-internal-queue.md`
- `docs/reference/heartbeat/configuring-internal-queue.md`
- `docs/reference/auditbeat/configuring-internal-queue.md`
- `docs/reference/packetbeat/configuring-internal-queue.md`
- `docs/reference/winlogbeat/configuring-internal-queue.md`

## Suggested Actions

- [ ] Add a `queue.slab` section (purpose, selection syntax, supported options such as `events`, and behavior differences vs `queue.mem`/`queue.disk`) to the Beat internal queue docs.
- [ ] Add a minimal configuration example showing `queue.slab` in beat YAML.
- [ ] Verify generated/reference docs for all Beats include the new queue type consistently.

> [!NOTE]
>
> 🔒 Integrity filter blocked 11 items
>
> The following items were blocked because they don't meet the GitHub integrity level.
>
> - [#51058](https://github.com/elastic/beats/pull/51058) `search_pull_requests`: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".
> - [#51057](https://github.com/elastic/beats/pull/51057) `search_pull_requests`: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".
> - [#51056](https://github.com/elastic/beats/pull/51056) `search_pull_requests`: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".
> - [#51116](https://github.com/elastic/beats/pull/51116) `search_pull_requests`: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".
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> - [#51118](https://github.com/elastic/beats/pull/51118) `search_pull_requests`: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".
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> - [#50808](https://github.com/elastic/beats/pull/50808) `search_pull_requests`: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".
> - [#50475](https://github.com/elastic/beats/pull/50475) `search_pull_requests`: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".
> - [#50140](https://github.com/elastic/beats/pull/50140) `search_pull_requests`: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".
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>
> To allow these resources, lower `min-integrity` in your GitHub frontmatter:
>
> ```yaml
> tools:
> github:
> min-integrity: approved # merged | approved | unapproved | none
> ```
>
>

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