Add historic data ingestion support to prometheus-pusher

This commit extends prometheus-pusher to support ingesting historic data
with custom timestamps via Prometheus Remote Write API.

## Key Changes

1. New Historic Data Module (historic.go)
   - GenerateHistoricMetrics: Creates metrics for specific past timestamps
   - PushHistoricData: Sends single datapoint via Remote Write API
   - BackfillHistoricData: Backfills range of historic data
   - Uses Protobuf + Snappy encoding per Prometheus spec

2. Enhanced Main Binary (main.go, realtime.go)
   - Refactored to support multiple modes
   - Mode 1: realtime - Push to Pushgateway (original behavior)
   - Mode 2: historic - Push single historic datapoint
   - Mode 3: backfill - Backfill range of historic data
   - Command-line flags for configuration

3. Prometheus Configuration (persistence-values.yaml)
   - Added web.enable-remote-write-receiver flag
   - Enables Prometheus to accept timestamped samples via Remote Write API
   - Required for historic data ingestion

4. Documentation (HISTORIC.md)
   - Complete guide for historic data ingestion
   - Explains limitations and best practices
   - Examples for all three modes
   - Troubleshooting guide

## Technical Details

**Problem**: Pushgateway doesn't support custom timestamps - Prometheus
always uses "now" when scraping. This prevents backfilling historic data.

**Solution**: Use Prometheus Remote Write API which accepts timestamped
samples. Requires enabling --web.enable-remote-write-receiver flag.

**Data Format**: Protobuf (prompb.WriteRequest) with Snappy compression

**Use Cases**:
- Backfill missing data (e.g., during outage)
- Import historic data from other systems
- Testing with specific timestamps
- Data migration scenarios

## Usage Examples

```bash
# Realtime mode (original behavior)
./prometheus-pusher-historic -mode=realtime -continuous

# Push data from 24 hours ago
./prometheus-pusher-historic -mode=historic -hours-ago=24

# Backfill last 48 hours with 1-hour intervals
./prometheus-pusher-historic -mode=backfill -start-hours=48 -end-hours=0 -interval=1
```

## Dependencies Added
- github.com/prometheus/prometheus (for prompb package)
- github.com/golang/snappy (for compression)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

1 files changed, 16 insertions, 7 deletions

diff --git a/f3s/prometheus-pusher/go.mod b/f3s/prometheus-pusher/go.mod
index 4576c38..e5fbf08 100644
--- a/f3s/prometheus-pusher/go.mod
+++ b/f3s/prometheus-pusher/go.mod
@@ -1,16 +1,25 @@
 module prometheus-pusher
 
-go 1.21
+go 1.24.0
 
-require github.com/prometheus/client_golang v1.20.5
+require (
+	github.com/golang/snappy v1.0.0
+	github.com/prometheus/client_golang v1.23.2
+	github.com/prometheus/prometheus v0.308.1
+)
 
 require (
 	github.com/beorn7/perks v1.0.1 // indirect
 	github.com/cespare/xxhash/v2 v2.3.0 // indirect
+	github.com/gogo/protobuf v1.3.2 // indirect
+	github.com/grafana/regexp v0.0.0-20250905093917-f7b3be9d1853 // indirect
+	github.com/kr/text v0.2.0 // indirect
 	github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 // indirect
-	github.com/prometheus/client_model v0.6.1 // indirect
-	github.com/prometheus/common v0.55.0 // indirect
-	github.com/prometheus/procfs v0.15.1 // indirect
-	golang.org/x/sys v0.22.0 // indirect
-	google.golang.org/protobuf v1.34.2 // indirect
+	github.com/prometheus/client_model v0.6.2 // indirect
+	github.com/prometheus/common v0.67.4 // indirect
+	github.com/prometheus/procfs v0.16.1 // indirect
+	go.yaml.in/yaml/v2 v2.4.3 // indirect
+	golang.org/x/sys v0.37.0 // indirect
+	golang.org/x/text v0.30.0 // indirect
+	google.golang.org/protobuf v1.36.10 // indirect
 )