GeoIP processor: Option to enable private IP address lookups #6079

Is your feature request related to a problem? Please describe.
Currently, the GeoIP processor in Data Prepper ignores private IP addresses. This makes it difficult to enrich internal network traffic (e.g., NetFlow or audit logs) with metadata from an internal IP Address Management (IPAM) system, such as office, datacenter, or department information

Describe the solution you'd like
Introduce a configuration option in the geoip_service that allows processing of private IP addresses. For example:

extensions:
  geoip_service:
    maxmind:
      lookup_private_addresses: true

This would require an update to GeoInetAddress.java

class GeoInetAddress {

    static Optional<InetAddress> usableInetFromString(final String ipAddress) {
        final InetAddress address;
        try {
            address = InetAddresses.forString(ipAddress);
        } catch (final IllegalArgumentException e) {
            return Optional.empty();
        }
        if (isPublicIpAddress(address) OR LOOKUP_PRIVATE_ADDRESS)
            return Optional.of(address);
        return Optional.empty();
    }

Describe alternatives you've considered (Optional)
An alternative is to use the add_entries processor in combination with add_when and cidrContains()
However, this approach is significantly slower and becomes impractical with large numbers of CIDR ranges, especially for NetFlow enrichment.

Additional context
It is straightforward to enrich MMDB files with internal IPAM data using scripts like
Enriching MMDB files with your own data using Go

As a further enhancement, it would be useful to allow reading custom fields from MMDB files (not only geo-related data). This would make it possible to attach metadata such as department or business unit information to a given CIDR block.