feat: add Elasticsearch monitoring dashboard

[Krishna1186]

Summary

Adds a comprehensive Elasticsearch monitoring dashboard using metrics from the OpenTelemetry Elasticsearch receiver.

4 sections, 20 panels:

• Node Metrics — Disk total/free/available, OS CPU usage, JVM heap and non-heap memory (grouped by node)
• Cluster Health — Health status (green/yellow/red), active/unassigned shards, pending tasks, total nodes, in-flight fetches
• Index Metrics — Document count and shard size per index
• Query & Request Metrics — Query/fetch/index operation rates and latencies

All metric names sourced directly from the OTel Elasticsearch receiver metadata.yaml.

Fixes SigNoz/signoz#6010

[bengivre]

Not sure where to mention this. I have installed the dashboards and it works well, great job , thanks.
There is just 3 panels that needs to be adjusted :

Panel 1 & 2 — elasticsearch.cluster.shards
# Remove:

shard_state = 'active'
shard_state = 'unassigned'

# Replace with:

state = 'active'
state = 'unassigned'

Panel 3 — elasticsearch.index.documents
# Remove:

document_state = 'active'

# Replace with:
state = 'active'