Feature Request: Configurable TTL for ClickHouse system log tables via `values.yaml`

There is currently no way to configure TTL for ClickHouse internal system log tables (e.g. `trace_log`, `query_log`, `metric_log`) through the Helm chart's `values.yaml`. This causes those tables to grow unbounded, which can fill up the data PVC and corrupt user data tables.

## Problem

ClickHouse system log tables such as `trace_log`, `query_log`, `metric_log`, and others do not have a TTL configured by default. In a production deployment, these tables accumulate data indefinitely.

In our case, `system.trace_log` grew to **~97 GB** over roughly 6 weeks, completely filling the `/var/lib/clickhouse` PVC (108 GB). This caused ClickHouse to fail writing new data parts, which resulted in 125+ broken parts across user tables (`otel_traces`, `otel_traces_trace_id_ts`), preventing those tables from loading entirely and making HyperDX show no data at all.

The affected system tables and their observed sizes at the time of the incident:

| Table | Size |
|---|---|
| `trace_log` | ~97 GB (dominant) |
| `query_log` | 2.84 GB |
| `part_log` | 1.67 GB |
| `processors_profile_log` | 972 MB |
| `metric_log` | 652 MB |
| `asynchronous_metric_log` | 248 MB |

## Expected Behavior

The Helm chart should expose a configuration option to set TTL for system log tables, so that operators can define retention policies without having to manually run `ALTER TABLE` commands after every deployment or upgrade.

## Suggested Implementation

Add a `systemLogs` block under `clickhouse.config` in `values.yaml`:

```yaml
clickhouse:
config:
systemLogs:
ttlDays: 7 # Set to 0 to disable TTL
```

And reflect it in the `clickhouse-configmap.yaml` template:

```xml

system
trace_log
toYYYYMM(event_date)
7500
{{- if gt .Values.clickhouse.config.systemLogs.ttlDays 0 }}
event_date + INTERVAL {{ .Values.clickhouse.config.systemLogs.ttlDays }} DAY DELETE
{{- end }}

```

This pattern would apply to all system log tables already declared in the configmap (`query_log`, `metric_log`, `asynchronous_metric_log`, `part_log`, `processors_profile_log`, `trace_log`, `query_thread_log`, `query_views_log`, `opentelemetry_span_log`).

## Workaround

Until this is supported, TTL must be applied manually via `clickhouse-client` after each deployment:

```sql
ALTER TABLE system.trace_log MODIFY TTL event_date + INTERVAL 7 DAY DELETE;
ALTER TABLE system.query_log MODIFY TTL event_date + INTERVAL 7 DAY DELETE;
ALTER TABLE system.part_log MODIFY TTL event_date + INTERVAL 7 DAY DELETE;
ALTER TABLE system.processors_profile_log MODIFY TTL event_date + INTERVAL 7 DAY DELETE;
ALTER TABLE system.metric_log MODIFY TTL event_date + INTERVAL 7 DAY DELETE;
ALTER TABLE system.asynchronous_metric_log MODIFY TTL event_date + INTERVAL 7 DAY DELETE;
ALTER TABLE system.query_views_log MODIFY TTL event_date + INTERVAL 7 DAY DELETE;
ALTER TABLE system.opentelemetry_span_log MODIFY TTL finish_date + INTERVAL 7 DAY DELETE;
```

Note that these changes do not persist if the pod is replaced with a fresh PVC, making automation through the chart the only reliable solution.

## Environment

- Chart version: `clickstack-1.1.2`
- App version: `2.19.0`
- ClickHouse image: `clickhouse/clickhouse-server:25.7-alpine`
- Kubernetes: OKE (Oracle Kubernetes Engine)