Add Grafana dashboard for monitoring Litestream metrics (#737)

Co-authored-by: Claude <[email protected]>

Author: corylanou

grafana/README.md

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+# Litestream Grafana Dashboard
+
+This directory contains a Grafana dashboard for monitoring Litestream metrics.
+
+## Prerequisites
+
+1. Litestream configured with metrics endpoint enabled in `litestream.yml`:
+
+   ```yaml
+   addr: ":9090"
+   ```
+
+2. Prometheus configured to scrape Litestream metrics:
+
+   ```yaml
+   scrape_configs:
+     - job_name: 'litestream'
+       static_configs:
+         - targets: ['localhost:9090']
+   ```
+
+3. Grafana with Prometheus data source configured
+
+## Installation
+
+1. Open Grafana and navigate to **Dashboards** → **Import**
+2. Upload the `litestream-dashboard.json` file or paste its contents
+3. Select your Prometheus data source
+4. Click **Import**
+
+## Metrics Included
+
+The dashboard monitors the following key metrics:
+
+- **Database & WAL Size**: Current size of the database and Write-Ahead Log
+- **Total WAL Bytes Written**: Cumulative bytes written to shadow WAL
+- **Sync Operations**: Rate of sync operations and any sync errors
+- **Sync Duration**: Time spent syncing shadow WAL
+- **Checkpoint Operations**: Rate of checkpoint operations by mode
+- **Checkpoint Errors**: Any checkpoint errors that occur
+- **Transaction ID**: Current transaction ID for each database
+- **Replica Operations**: Operations performed by replica type (GET/PUT)
+- **Replica Throughput**: Bytes transferred by replica operations
+
+## Configuration
+
+The dashboard uses template variables:
+
+- `datasource`: Select your Prometheus data source
+- `job`: Select the Prometheus job name (defaults to "litestream")
+
+## Support
+
+For issues or improvements to this dashboard, please open an issue at:
+<https://github.com/benbjohnson/litestream/issues>