Deprecate Adapter\HttpDiscovery

[smaddock]

Is your feature request related to a problem? Redundant code. Currently the OpenTelemetry\SDK\Common\Adapter\HttpDiscovery and OpenTelemetry\SDK\Common\Http\Psr namespaces have overlapping functionality.

• Http\Psr has more features than Adapter\HttpDiscovery, namely forwarding client options to well-known implementations.
• Outside their own namespaces:
  • Http\Psr is used in multiple places, e.g., PsrTransportFactory and (ironically?) Adapter\HttpDiscovery
  • Adapter\HttpDiscovery is only used in OpenTelemetry\Contrib\Otlp\HttpEndpointResolver, where it could be replaced (see below).
• Overlaps:
  • Http\Psr\Client\Discovery replaces Adapter\HttpDiscovery\PsrClientResolver directly
  • Http\Psr\Message\MessageFactory could easily be expanded with defaults to make Adapter\HttpDiscovery\MessageFactoryResolver obsolete, without breaking any existing uses of MessageFactory
  • Adapter\HttpDiscovery\DependencyResolver and Adapter\HttpDiscovery\HttpPlugClientResolver have no direct replacements, although their interfaces are in Http, but I also can't find any instances of them being used.

Describe the solution you'd like Deprecate Adapter\HttpDiscovery:

• Add the above mentioned functionality to Http\Psr\Message\MessageFactory
• Replace the single existing usage of Adapter\HttpDiscovery\MessageFactoryResolver with the expanded MessageFactory
• Update all tests
• Add a @deprecated PHPDoc tag (or #[Deprecated] attribute >= PHP 8.4) to the Adapter\HttpDiscovery classes naming their replacements
• Remove the class entirely in open-telemetry/sdk 2.0

Describe alternatives you've considered I could find no uses of either namespace in opentelemetry-php-contrib. I also searched GitHub for those namespaces and could not find any additional uses outside of the core opentelemetry-php repo and it's forks.

Additional context I'm working on another contrib component, and didn't want to make a hard-requirement on third-party libraries outside of psr/http-client-implementation and psr/http-factory-implementation. I figured there was likely a shared internal component already built out, and behold, there are two!

I'm happy to take a stab at a PR if the maintainers agree, but I wanted to ask if there was intent or backstory I was unaware of before I spent time on it.

[brettmc]

I agree with this approach. Adapter\HttpDiscovery has been slowly whittled down for a while, and a lot of dead code there has already been removed.