make tracing defaults consistent

[wkloucek]

ocis and proxy are the only extensions which have a default for tracing endpoints. There shouldn't be a default at all, because there is a comparison if OCIS_TRACING_COLLECTOR is empty:

ocis/proxy/pkg/command/server.go

Lines 81 to 89 in a591d65

	exporter, err := jaeger.NewExporter(
	jaeger.Options{
	AgentEndpoint: cfg.Tracing.Endpoint,
	CollectorEndpoint: cfg.Tracing.Collector,
	Process: jaeger.Process{
	ServiceName: cfg.Tracing.Service,
	},
	},
	)

Which calls this: https://github.com/census-ecosystem/opencensus-go-exporter-jaeger/blob/30c8b0fe8ad9d0eac5785893f3941b2e72c5aaaa/jaeger.go#L88-L98

For example if you want to use OCIS_TRACING_ENDPOINT at the moment you have to explicitly override OCIS_TRACING_COLLECTOR with an empty string. The configuration looks like this:

export OCIS_TRACING_COLLECTOR=""
export OCIS_TRACING_ENABLED=true
export OCIS_TRACING_ENDPOINT=127.0.0.1:6831

After the merge this would look like this:

export OCIS_TRACING_ENABLED=true
export OCIS_TRACING_ENDPOINT=127.0.0.1:6831

Loosely related: cs3org/reva#1379

[update-docs]

Thanks for opening this pull request! The maintainers of this repository would appreciate it if you would create a changelog item based on your changes.

[sonarqubecloud]

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