Documentation: Clarify that notification suffix filtering is not supported by GCS API

### Environment details

- **OS**: Linux
- **Python version**: 3.11
- **google-cloud-storage version**: 3.4.0

### Summary

The `bucket.notification()` method does not support suffix filtering (e.g., `object_name_suffix` or `blob_name_suffix` parameters), which can lead to confusion when users attempt to create notifications that only trigger for files ending with specific suffixes like `.json` or `UploadCompleted.json`.

While this is a **limitation of the underlying GCS JSON API v1** (which only supports `object_name_prefix` in the [[notification resource schema](https://cloud.google.com/storage/docs/json_api/v1/notifications)](https://cloud.google.com/storage/docs/json_api/v1/notifications)), the Python client library documentation could be clearer about this limitation.

### Problem

Users attempting to filter GCS notifications by file suffix may try approaches like:

```python
notification = bucket.notification(
topic_name="my-topic",
blob_name_prefix="", # This works
# How do I filter by suffix? ❌ Not possible
)
```

The `bucket.notification()` signature shows only `blob_name_prefix` is available:

```python
def notification(
self,
topic_name=None,
topic_project=None,
custom_attributes=None,
event_types=None,
blob_name_prefix=None, # ← Only PREFIX supported
payload_format=NONE_PAYLOAD_FORMAT,
notification_id=None,
):
```

### Current Workarounds

Users must filter notifications in their application code:

```python
def process_notification(event):
# Application-level filtering since GCS doesn't support suffix
if not event.name.endswith("UploadCompleted.json"):
return # Skip non-sentinel files

# Process the notification
...
```

### Requested Changes

**Option 1: Add documentation note** (Minimal change)

Add a note to the `BucketNotification` class docstring and `bucket.notification()` method:

```python
def notification(...):
"""Factory: create a notification resource for the bucket.

Note: The GCS Notification API only supports prefix filtering via
blob_name_prefix. Suffix filtering (e.g., only notify for files
ending with '.json') is not supported by the GCS API. Applications
must implement suffix filtering in their notification handlers.

See: https://cloud.google.com/storage/docs/json_api/v1/notifications
"""
```

**Option 2: Add to samples** (Better)

Create a sample showing the recommended pattern for suffix-based filtering:

`samples/snippets/notification_with_suffix_filter.py`:
```python
"""Demonstrates application-level suffix filtering for GCS notifications.

Since GCS notifications only support prefix filtering, applications that
need to trigger only on specific file extensions must filter in code.
"""

def process_pubsub_notification(message):
"""Process Pub/Sub message with suffix filtering."""
import json
import base64

# Decode the GCS event
data = base64.b64decode(message.data).decode('utf-8')
event = json.loads(data)

object_name = event['name']

# Application-level suffix filtering
if not object_name.endswith('UploadCompleted.json'):
print(f"Skipping non-sentinel file: {object_name}")
message.ack()
return

# Process the sentinel file
print(f"Processing upload completion: {object_name}")
# ... your processing logic ...
message.ack()
```

### Why This Matters

This is a common pain point for users building event-driven pipelines. Many workflows need to trigger on specific sentinel files (like `UploadCompleted.json`, `_SUCCESS`, `manifest.json`) rather than every intermediate file upload.

Without clear documentation, users waste time trying to:
1. Find the "right" parameter name for suffix filtering
2. Debug why `_properties["objectNameSuffix"]` doesn't work
3. Upgrade library versions thinking it's a bug
4. File support tickets or Stack Overflow questions

### Related Issues

- googleapis/python-storage#1035 - Users requesting `matchGlob` for similar filtering needs
- This pattern appears in discussions about notification filtering across various forums

### Additional Context

The GCS REST API notification schema does not include `objectNameSuffix`:
- ✓ Supported: `object_name_prefix`
- ✗ Not supported: `object_name_suffix`

This appears to be an intentional design decision by the GCS team (prefix filtering is efficient with GCS's internal indexing, while suffix filtering would require scanning all object names).