Allow to disable plugin via environment variable

[vmarchaud]

When discussing about the unpatch method of each plugin, i said that which make me think that it would be useful to disable plugin but via environemnt variable.

The use cases is pretty simple: modifying the code can take more than 10min for some CI setup (time to rebuild, push images etc) so removing plugins can take quite some times.
Having a environment variable to do that allows engineer to test out quickly by just re-deploying their app.

Datadog actually implemented that recently: DataDog/dd-trace-js#733 so i believe i'm not the only one having this need.

WDYT ?

[dyladan]

I think we should wait for the named tracer PR to merge since this is the use case it is designed for

[markwolff]

Is this ready to be looked at now? This is something I am interested in as well so I can stub something out if you haven't already @vmarchaud. I also think a separate environment variable to disable all plugins would be useful here.

[vmarchaud]

@markwolff I didnt started any work on that so you can do it if you want to :)

[dyladan]

I'd say go for it