dependencies api: Add observability

Created by: efritz

This adds tracing, metrics, and hooks for sentry (If we configure it later) by wrapping the dependencies API with observability package goodies.

This updates the search client to construct a global singleton on first access with a single instance of metrics. In the future we'll need to ensure that we create as few distinct APIs as possible to maximize bulk operations and caching benefits.

Test plan

Tested by hand and gotted u a pretty picture (see PR description)!