Add support for `AlwaysRecord` sampler

[vitorvasc]

Description

The latest OpenTelemetry Specification version introduced the AlwaysRecord sampler:

AlwaysRecord is a sampler decorator that ensures every span is passed to
the SpanProcessor, even those that would normally be dropped. It does this
by converting DROP decisions from the wrapped sampler into RECORD_ONLY
decisions, allowing processors to see all spans without sending them to
exporters. This is typically used to enable accurate span-to-metrics processing.

References:

• https://opentelemetry.io/docs/specs/otel/trace/sdk/#alwaysrecord
• Always process spans / AlwaysRecord Sampler opentelemetry-specification#4698
• Add spec for AlwaysRecord sampler opentelemetry-specification#4699

[vitorvasc]

If this issue is ready to be addressed and there are no blockers, I'd love to work on it and submit a PR!

[dmathieu]

I don't believe there are any blockers to doing this.