This PR adds a new configuration block specifically for the otelhttp
instrumentation. This block is separate from the existing
"opentelemetry" configuration, and is only relevant when using otelhttp
instrumentation. It does not share any codepath with the existing
configuration, so it is at the top level to indicate which services it
applies to.
There's a bit of plumbing new configuration through. I've adopted the
measured_http package to also set up opentelemetry instead of just
metrics, which should hopefully allow any future changes to be smaller
(just config & there) and more consistent between the wfe2 and ocsp
responder.
There's one option here now, which disables setting
[otelhttp.WithPublicEndpoint](https://pkg.go.dev/go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp#WithPublicEndpoint).
This option is designed to do exactly what we want: Don't accept
incoming spans as parents of the new span created in the server.
Previously we had a setting to disable parent-based sampling to help
with this problem, which doesn't really make sense anymore, so let's
just remove it and simplify that setup path. The default of "false" is
designed to be the safe option. It's set to True in the test/ configs
for integration tests that use traces, and I expect we'll likely set it
true in production eventually once the LBs are configured to handle
tracing themselves.
Fixes#6851
3aae67b8a9