opentelemetry-collector: use full contrib distribution

Created by: bobheadxi

Most crucially, the contrib distribution includes the gcloud exporter we want to trial, and in the grand scheme of things we want to maximize out-of-the-box usability for potential customers that use this so I think it best we just use the full contrib distribution of the collector.

Since this is a significantly larger image, I've removed the --no-cache argument from the build script.

Test plan

build locally, sg start otel