Add PebbleLogForwarder to the otlp library

[Copilot]

The otlp interface lacks a K8s log forwarding utility analogous to LogForwarder in loki_push_api. Charms transitioning from loki_push_api to otlp need a way to configure Pebble's native log forwarding to OTLP endpoints.

Changes

• _log_forwarder.py: New PebbleLogForwarder class with a build_otlp_layer() static method that converts OtlpRequirer.endpoints into a Pebble Layer with type: opentelemetry log targets. Only endpoints advertising "logs" telemetry are included. Optional JujuTopology injects COS-standard labels.
• __init__.py: Export PebbleLogForwarder, add usage documentation for K8s charms.
• test_log_forwarder.py: 10 unit tests covering single/multiple endpoints, topology labels, telemetry filtering, enable/disable targets.

Usage

from charmlibs.interfaces.otlp import OtlpRequirer, PebbleLogForwarder
from cosl.juju_topology import JujuTopology

endpoints = OtlpRequirer(charm, protocols=["http"], telemetries=["logs"]).endpoints
layer = PebbleLogForwarder.build_otlp_layer(
    endpoints, topology=JujuTopology.from_charm(self),
)
container.add_layer(f"{container.name}-log-forwarding", layer, combine=True)

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• documentation.ubuntu.com
  • Triggering command: /home/REDACTED/work/_temp/ghcca-node/node/bin/node /home/REDACTED/work/_temp/ghcca-node/node/bin/node --enable-source-maps /home/REDACTED/work/_temp/copilot-developer-action-main/dist/index.js (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)