otel: bundle probabilistic sampling processor

Created by: jhchabran

This PR add the probabilistic sampling processor to our otel collector packaged image. This allows customers to enable probabilistic sampling without having to rebuild the docker image of the collector on their own.

Part of #40813 (closed) and #37958 (closed)

⚠️ It is to be noted that if enabled, the sampling processor completely disregard selective tracing at this stage. See #41177 for the issue tracking this.

Fixes https://github.com/sourcegraph/sourcegraph/pull/41176

Test plan

Ran the collector locally with the configuration that is presently commented. Traces will be discarded until they get picked by the processor. We get complete traces of courses, no spans are missing.