Add a `LogForwarder` component in the `otlp` library

The [otlp](https://github.com/canonical/charmlibs/tree/main/interfaces/otlp) interface currently lacks a `LogForwarder` class (similar to the one in [loki_push_api](https://github.com/canonical/opentelemetry-collector-operator/blob/3c976e9ddcb44081fa907f768c03a4fd1d9cb3ff/lib/charms/loki_k8s/v1/loki_push_api.py#L361)) for K8s charms to automatically configure their pebble to consume the endpoint received in the `otlp` relation and forward logs to the endpoint.

If the goal of the new `otlp` interface is to replace `loki_push_api` and `metrics_endpoint` interface, we should ideally have this `LogForwarder` class. A lot of charms currently use the `loki_push_api` interface, especially the `LogForwarder` class. Some examples are : [opencti-operator](https://github.com/canonical/opencti-operator), [paas-charm](https://github.com/canonical/paas-charm), [oauthkeeper](https://github.com/canonical/oathkeeper-operator) etc.

If we want these charms to be able to transition to the new `otlp` interface easily, providing some support to automatically configure sending logs to the provider charms would be useful.

One thing to consider is that the `otlp` interface can be used by both the machine and k8s charms, so we might need to have some gatekeeping logic on preventing machine charms from using this class?