fix: disable keep-alives for internal traffic

[swiatekm]

Disable HTTP keep-alives for network traffic from collectors to metadata enrichment. This should make the Kubernetes iptables-based load balancing work better at the cost of increased network traffic.

Checklist

• Changelog updated or skip changelog label added
• Documentation updated
• Template tests added for new features
• Integration tests added or modified for major features

[andrzej-stencel]

Note for future us: This change applies to both logs-collector and metrics-collector. It does not apply to Prometheus as metrics collector, which still needs the remote write proxy for proper load balancing.