OpenTelemetry exporters documentation improvements

[brunobat]

• Fixes: "Provider io.opentelemetry.exporter.otlp.internal.OtlpSpanExporterProvider not found" #48438
• Fixes: Quarkus fails to start up if I set quarkus.otel.traces.exporter=otlp #48570

[geoand]

If the value is not supported, we should update the config to indicate that and also provide a good error message

[quarkus-bot]

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It should be safe to merge provided you have a look at the other checks in the summary.

[github-actions]

🎊 PR Preview 18d8e42 has been successfully built and deployed to https://quarkus-pr-main-48580-preview.surge.sh/version/main/guides/

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[spio]

Hi, Bruno.

It seems good to me.

I would suggest some more changes to the docs:

• In the description of the "quarkus.otel.traces.exporter" property (under both titles "OpenTelemetry Configuration Reference" and "Disable all or parts of the OpenTelemetry extension"), I think that the "otlp" option shoud be removed as a valid value, because it is not.
• By removing that value, the new section "The OpenTelemetry OTLP exporter" it's not necessary; in fact, it seems too severe to me to say "This is currently not supported in quarkus"; perhaps stating that "this is used by default in Quarkus" instead of that sentence is a little more polite.
• I think that adding a quick link to database tracing there could be useful.

And one last thing, but it is not fully related to this: it seems strange to me that, by default, direct jdbc connections are not traced by default (i.e. quarkus.datasource.jdbc.telemetry=false), but reactive connections are (quarkus.otel.instrument.vertx-sql-client=true). By the way, if you can, I would suggest to also modify the Quarkus Datasource config docs (https://es.quarkus.io/guides/datasource) to show, under the "Datasource tracing" title, that each datasource can be configured using "quarkus.datasource..jdbc.telemetry=true", as it is shown under "Datasource health check", "Datasource metrics" and "Narayana transaction manager integration".

Regards.