Support for suppressing instrumentation for specific scopes

[atheriel]

Follow-up on r-lib/httr2#729 (review).

I don't see anything in the OTel spec specifically for suppressing instrumentation from specific scopes (i.e. packages in our case), but I notice that the Java implementation supports it, as does Logfire.

We could have a language-specific configuration extension for this, e.g.

OTEL_R_SUPPRESS_SCOPES=httr2,ellmer

[atheriel]

This could belong in otelsdk rather than otel, too.

[gaborcsardi]

You mean suppress collecting traces etc.?

Automatic instrumentation is off for all packages, and you can opt in package by package.

[atheriel]

No, I mean specifically to disable traces, etc. purposefully emitted by that package via otel::start_span() and friends. So if users think that e.g. httr2 is too chatty, they can disable tracers for httr2 and httr2 only.

[gaborcsardi]

Right, disable exporting.

Instrumentation is adding the otel calls to your code, either manually or automatically.