[text-auditor] Fix clear Filebeat reference-doc grammar and typo text

## Text Improvements

The following user-facing text issues were found in the repository. Each is a low-effort fix.

### 1. Repeated grammar + typo in Filebeat input explanation paragraphs

**File:** `docs/reference/filebeat/filebeat-input-gcs.md` (line 55)
**Current text:** `Each of these buckets have their own attributes ... For now lets try to understand how this config works.`
**Suggested fix:** `Each of these buckets has its own attributes ... For now let's try to understand how this config works.`
**Why:** Clear subject-verb agreement error (`buckets have`) and missing apostrophe (`lets`) in user-facing docs.

**File:** `docs/reference/filebeat/filebeat-input-azure-blob-storage.md` (line 52)
**Current text:** `Each of these containers have their own attributes ... For now lets try to understand how this config works.`
**Suggested fix:** `Each of these containers has its own attributes ... For now let's try to understand how this config works.`
**Why:** Same repeated grammar/typo family in a second user-facing docs page.

### 2. Grammar error in multiline option description

**File:** `docs/reference/filebeat/multiline-examples.md` (line 60)
**Current text:** `... and while_pattern which aggregate lines by pattern without match option.`
**Suggested fix:** `... and while_pattern which aggregates lines by pattern without a match option.`
**Why:** Clear subject-verb agreement error (`which aggregate`) and missing article in user-facing docs.

## Suggested Actions

- [ ] Update both Filebeat input docs (`filebeat-input-gcs.md`, `filebeat-input-azure-blob-storage.md`) to use `has its own` and `let's` in the explanation paragraph.
- [ ] Update `docs/reference/filebeat/multiline-examples.md` to use `which aggregates ... without a match option` for grammatical correctness.

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> - [x] expires on Aug 25, 2026, 1:34 PM UTC

Open docs/reference/filebeat/filebeat-input-gcs.md, docs/reference/filebeat/filebeat-input-azure-blob-storage.md, and docs/reference/filebeat/multiline-examples.md at the referenced paragraphs. Apply the specified grammar and typo corrections, then verify all three user-facing passages use the requested wording.

Written by the indexing model from the issue text.