Removed deprecated loglevel in otel-collector config

[madwort]

loglevel is deprecated

https://github.com/open-telemetry/opentelemetry-collector/blob/v0.71.0/exporter/loggingexporter/README.md#note

we use the same var elsewhere tho, so needs a tiny bit of rework

[alarthast]

As of otel/opentelemetry-collector-contrib v0.111.0 the logging exporter has been removed.

We should either suppress dependabot PRs for otel/opentelemetry-collector-contrib, or switch to using the debug exporter with verbosity (see #220; we will also need to check for use cases on dokku4, perhaps?)

[suzannehamilton]

Simon tried to do this six months ago and it wasn't trivial.

[bloodearnest]

There is a non-trivial test suite for this, which spins up two instances of otel-gateway to test our configuration actually forwards telemetry correctly.

However, it currently not working x-platform reliably: #180. It seems to be todo with docker compose networking differences.

Additionally, the test suite is out of date

• uses python3.8
• no formal dependency pinning, uses latest versions.

It does still pass on main in CI however: https://github.com/opensafely-core/sysadmin/actions/runs/13073273944, but not locally for me or @alarthast OOTB.

So I think that we'd first need to

• make sure the test-ci invocation works locally on linux and mac (Fix test-ci locally #180)
• update the tests suite to use more recent python and pin deps (probably use uv?)

Then, migrating the config should be practical.