Set request context before recording metrics

[ahus1]

Closes #5355

Motivation:

This sets the context so that the logic in Quarkus will know that this call is traced via OpenTracing, and then records and exemplar for the metrics.

I've been monkey-patching Keycloak 26 with a changed Http1xServerConnection#reportResponseComplete() and it worked for me in in a manual test.

I've been looking for other places of metrics.requestReset() and metrics.responseEnd() and fixing them the same way.

Draft PR for now, as I didn't add any tests, and would probably need help writing some if they would be required. Also waiting for a results that the build returns.

Conformance:

You should have signed the Eclipse Contributor Agreement as explained in https://github.com/eclipse/vert.x/blob/master/CONTRIBUTING.md
Please also make sure you adhere to the code style guidelines: https://github.com/vert-x3/wiki/wiki/Vert.x-code-style-guidelines

[ahus1]

I've added a reproducer in https://github.com/ahus1/quarkus-otel-missing-examplar-example

Not sure how to best add a test case for that. I'd love to hear a hint on how to do that.

[tsegismont]

@ahus1 see my comments in quarkusio/quarkus#43845 and #5355 (rescheduling the task on the context bound to the request is not a good option).

[ahus1]

Changing this to draft, and will probably close it as it is likely to be handled on the Quarkus side

[ahus1]

Closing as it will be handled on the Quarkus side. Sorry for the noise!