Stabilize new attribute value types and limits

[pellared]

Stabilize the new attribute values and limits added in:

• Extend the set of attribute value types #4651

Following issues should be addressed before that:

• Clarify "ensure" in implemeting unique keys #4707
• Confusion that we have both map<string, AnyValue> and Attribute Collections #4708
• Reorder sections in specification/common/README.md #4709

[lmolkova]

Java implementation: open-telemetry/opentelemetry-java#7814 (no limits yet)

Update: Java implementation merged to incubating artifact

[pellared]

Go prototype: open-telemetry/opentelemetry-go#6809 (comment). No limits, yet approved by the Go SIG.