Bump semconv to the latest version

[pellared]

Problem Statement

Currently this and contrib repositories are using go.opentelemetry.io/otel/semconv/v1.17.0.

Proposed Solution

Bump the usage of semconv to the latest version (currently v1.21.0).

Other

Moreover, it would be good to look at these issues:

• Resource merge semantics make upgrades problematic #2341
• resource.Default()/etc is a footgun #3769
• Hard coding semconv.SchemaURL references, inconsistencies and brittleness opentelemetry-go-contrib#3657

Maybe we should document the troubleshooting for these scenarios and donate https://github.com/MrAlias/otel-schema-utils to https://github.com/open-telemetry/opentelemetry-go-contrib.