Allow suppressing nested activities in native instrumentations without dependency on OTel SDK

[lmolkova]

Feature Request

Native instrumentations cannot suppress underlying HTTP spans without taking a dependency on OTel. They also cannot enrich/improve generic HTTP spans.

Higher-level (than HTTP) Instrumentations such as Azure SDK, AWS, Elasticsearch clients may want to suppress default generic HTTP instrumentations. Here're the reasons they might not want default HTTP spans:

• too verbose. E.g. client library may want to report logical calls and supply all information there.
• add custom details:
  • in the case of Azure SDKs, we want to report x-ms-*request-id headers to correlate with server-side events
  • report better request duration - e.g. we know when stream reading is complete (see Disambiguate http.*.duriation and/or split them into separate metrics opentelemetry-specification#3520 discussion)
  • report better status: e.g. we may know when 404 or 409 represents/does not represent an error

Currently suppressing generic instrumentation is only possible with SuppressInstrumentationScope:

• Azure SDK native instrumentations cannot do it
• AWS, Elasticsearch instrumentations do it in instr libraries that depend on OTel.

Describe the solution you'd like:

Define a well-known key, which, when set in the Activity.Properties, suppresses the creation of nested activities. Example shown in #4642

Describe alternatives you've considered.

• Instrumentation layers and suppressing duplicates oteps#172 - introduced span type and suppressing duplicates based on type (implemented in Java, but too controversial and did not make it into the spec)
• providing a way to enrich generic HTTP spans
• reflection-based access to SuppressInstrumentationScope, which wouldn't work in the case of AOT

I'll be happy with any other solution that can be done without taking a dependency on OTel.

Additional Context

• Client libraries: Manual/programmatic and auto instrumentation duplication problem  opentelemetry-specification#1767