Differentiate between stable and experimental semantic conventions

[joaopgrassi]

Component

OpenTelemetry.SemanticConventions

Is your feature request related to a problem?

Currently, the semantic conventions package contains all attributes under the same namespace/place. With the stabilization of areas of semantic conventions (e.g., HTTP) semantic conventions should be split between the ones that are stable vs experimental.

Java and Python already are following this pattern of "incubating" for experimental ones. Examples can be found here of how the package is structured

https://github.com/open-telemetry/opentelemetry-python/pull/4091/files
open-telemetry/semantic-conventions-java#70

What is the expected behavior?

We should follow suit and organize the generated attributes under a new folder called "incubating" and maybe even under a different namespace. To be discussed with the group here what we prefer.

Which alternative solutions or features have you considered?

N/A

Additional context

N/A

[cijothomas]

Related: open-telemetry/opentelemetry-dotnet#4086