Extend configuration to support sending traces to Gitlab Observability Platform

Related to gitlab-org/opstrace/opstrace#1957 (closed)

Adds three new config options - OTEL endpoint, auth token, and CA cert for TLS verification plus makes changes in OTEL code initialization to support those.

From what I noticed some of the traces KAS is sending now need anchoring at root span, some of them are endless - have no proper termination:

Fixing it is outside of the scope of this MR. Please have a look at my MR for gitlab-development-kit. It outlines how to set up development environment for KAS+GOS, where you can iterate on the instrumentation code.

Tested locally using the steps outlined in gitlab-org/gitlab-development-kit!2883 (comment 1208258523)

PR deploying the change to production: gitlab-com/gl-infra/k8s-workloads/gitlab-com!2402 (merged) I do not know though if I need any extra steps to deploy it (make a release?).