Support complex attribute types #457
Description
As documented in https://opentelemetry.io/blog/2025/complex-attribute-types/ and in the spec in open-telemetry/opentelemetry-specification@110aed2 attributes now support complex types.
This is still marked as Development in https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/common/README.md, so we probably don't need to support it yet.