[processor/dnslookup] Initial implementation

[kaisecheng]

Description

This PR adds a new DNS Lookup processor for resolving hostnames to IP and reversing DNS lookups IP to hostname.

Resolution Order and Retry Mechanism

The processor implements a chain of resolvers with the following resolution order

1. Hostfiles - when hostname is not in files, the processor continues to the next resolver in the chain. Note that later hostfiles in the list take precedence over earlier ones for duplicate entries.
2. Custom DNS servers - "no resolution" is a valid result and the chain stops. For each DNS server, temporary failures trigger retries. The resolver prefers IPv4 addresses over IPv6 when both are available.
3. System resolver - same as (2), uses the operating system's default DNS as the final fallback

Caching

• Successful resolutions are cached in a "hit cache" with configurable TTL
• Failed lookups are cached in a "miss cache" to avoid repeated expensive failures
• Both caches implement LRU eviction policies

Config

  dnslookup:
    # Forward DNS resolution configuration (hostname to IP)
    # Default: enabled
    resolve:
      enabled: true
      # Context for attributes: "resource" or "record". Default: "resource"
      context: "record"
      # List of attributes to check for hostnames. The first valid hostname is used. Default: ["source.address"]
      attributes: ["source.address"]
      # Attribute to store the resolved IP.  Default: "source.ip"
      resolved_attribute: "source.ip"

    # Reverse DNS resolution configuration (IP to hostname)
    # Default: disabled
    reverse:
      enabled: true
      # Context for attributes: "resource" or "record". Default: "resource"
      context: "record"
      # List of attributes to check for IPs. The first valid IP is used. Default: ["source.ip"]
      attributes: ["server.ip"]
      # Attribute to store the resolved hostname. Default: "source.address"
      resolved_attribute: "server.address"

    # Maximum number of failed resolutions to cache. Default: 1000
    miss_cache_size: 1000
    # Time-to-live (seconds) for failed resolution cache entries. Default: 60
    miss_cache_ttl: 60
    # Maximum number of successful resolutions to cache. Default: 10000
    hit_cache_size: 10000 
    # Time-to-live (seconds) for successful resolution cache entries. Default: 300
    hit_cache_ttl: 300
    # Maximum number of retry attempts for DNS lookups. Default: 1
    max_retries: 1
    # Timeout (seconds) for individual DNS lookups. Default: 0.5
    timeout: 0.5
    
    # Path to custom host files. Default: []
    hostfiles: 
      - "/path/to/host/file"
      - "/path/to/other/file"
    
    # Address of custom DNS servers. Default: []
    nameservers:
      - 8.8.8.8
      - 1.1.1.1
    
    # Enable the system resolver. Default: true
    enable_system_resolver: true

Link to tracking issue

#34398

TODO

• tests for factory and prcoessor
• readme
• changelog

Testing

Added unit test for all resolvers

Documentation

cc @edmocosta