Add support for managing OpenTelemetry attributes

**Is your feature request related to a problem? Please describe.**

I'd like to be able to export logs to Grafana via the OpenTelemetry format and this [requires](https://grafana.com/docs/grafana-cloud/data-configuration/otlp/otlp-format-considerations/#logs) the ability to set OpenTelemetry attributes.

**Describe the solution you'd like**

I'd like the ability to both modify attributes as a filter and as part of the OpenTelemetry output.

**Describe alternatives you've considered**

I can use the Loki output but this isn't a documented log ingestion pattern in Grafana Cloud so support might be removed at any point.

**Additional context**