Update docs to include more details on Opentelemetry Collector

Our docs do mention [migrating from GA to Otelcol](https://documentation.ubuntu.com/observability/latest/how-to/migrate-gagent-to-otelcol/) but given that some users are already trying Otelcol, we should make an effort to provide more details regarding setting up Otelcol.
This effort should include roughly the following:
- Duplicating [the guide on integrating COS with non-charmed workloads](https://documentation.ubuntu.com/observability/latest/how-to/integrating-cos-lite-with-uncharmed-applications/) so a similar one exists for Otelcol.
- A more detailed guide on installing and configuring both the K8s and the machine charm.
- Otelcol should be listed under peripheral charms in the [list of charms references page](https://documentation.ubuntu.com/observability/latest/reference/charms/).
- The [integration matrix](https://documentation.ubuntu.com/observability/latest/reference/integration-matrix/) should be updated to include the snap where the GA snap is mentioned e.g. for logs and metrics