Suppressing Zipkin exporter's instrumentations

[LikeTheSalad]

Add instrumentation suppressing context key to the exporter. Similar to what was done for OkHttp-related exporters here.

[chungngoops]

I'm working on this issue.

[breedx-splk]

Hi @chungngoops . Any updates?

[chungngoops]

@breedx-splk : sorry I didn't have time to continue the work, but back on it now.

[SylvainJuge]

The way to suppress Zipkin exporter instrumentation might change a bit if #6546 is merged.

[chungngoops]

I created a draft PR #6552, I am struggling with creating test for the new changes, could anyone help me with this.

[breedx-splk]

I think this is done. @LikeTheSalad reopen if not the case. Thanks.