This injects trace context headers into requests to the auth hook,
allowing us to figure out how much time is spent here.
I added a basic tracing setup to the dev-auth-webhook, using
`tracing-util`, allowing me to verify that this works. This required
moving the Dockerfile to the root so the context contains the
`tracing-util` crate too.
I have also fixed the reference agent (by updating it), and patched our
Docker Compose files to correctly set up connectivity to Jaeger.
V3_GIT_ORIGIN_REV_ID: 2ff930bda4147d00dcc73268a814b08c8a07a359
