Expose subgraph logs via subgraph GraphQL

[fordN]

This PR introduces a more flexible subgraph log storage and querying system for Graph Node and enables subgraph logs to be queried through the GraphQL subgraph query API. The implementation supports multiple log storage backends (File, Elasticsearch, and Loki) with a consistent query interface exposed to users in the subgraph's GraphQL schema.

What's new

GraphQL Query API

• New _logs query field on all subgraph deployments
• Filter by log level, timestamp range, and text search
• Structured log entries with metadata (source location, arguments, subgraph ID)
• Support for pagination via first/skip parameters

Storage Backends

• File: JSON Lines format for local development (one file per subgraph)
• Elasticsearch: Enterprise search and analytics for production
• Loki: Grafana's lightweight log aggregation system
• Disabled: Default mode with no log storage overhead

Architecture

• LogDrain: Sink for writing logs to storage backends (File, Loki, Elasticsearch)
• LogStore: Read interface for querying logs from backends
• LoggerFactory: Refactored to support multi-backend log routing
• Configuration: Unified GRAPH_LOG_STORE_* environment variables with CLI argument parity

Examples

Querying logs

{
  _logs(
    level: ERROR
    search: "timeout"
    from: "2024-01-15T00:00:00Z"
    to: "2024-01-16T00:00:00Z"
    first: 100
  ) {
    id
    timestamp
    level
    text
    arguments {
      key
      value
    }
    meta {
      module
      line
      column
    }
  }
}

Configuring the logs store backend

File-based (development):

GRAPH_LOG_STORE_TYPE=file \
GRAPH_LOG_STORE_FILE_DIRECTORY=/var/log/subgraphs \
cargo run -p graph-node

Loki (production):

GRAPH_LOG_STORE_TYPE=loki \
GRAPH_LOG_STORE_LOKI_ENDPOINT=http://loki:3100 \
cargo run -p graph-node