Allow adding new attribute types

[pellared]

Follows https://github.com/open-telemetry/opentelemetry-specification/blob/main/oteps/4485-extending-attributes-to-support-complex-values.md

Communicate that we’ve revised the decision and will now allow the addition of new attribute types (which is not considered a major change):

• with end users via OTel blog post accompanied with draft PRs in proto (remove attribute restrictions) and spec (add new attribute types) and during conferences like KubeCon
• with OTel maitainers by creating issues in every language repo denoting change and requirements
  • Validate feasibility of supporting new attribute types opentelemetry-java#7621
  • Validate feasibility of supporting new attribute types opentelemetry-dotnet#6472
  • Validate feasibility of supporting new attribute types opentelemetry-python#4736
  • Validate feasibility of supporting new attribute types opentelemetry-js#5915
  • Validate feasibility of supporting new attribute types opentelemetry-php#1710
  • Validate feasibility of supporting new attribute types opentelemetry-erlang#895
  • Validate feasibility of supporting new attribute types opentelemetry-cpp#3632
  • Validate feasibility of supporting new attribute types opentelemetry-rust#3154
  • Validate feasibility of supporting new attribute types opentelemetry-swift#915
  • Validate feasibility of supporting new attribute types opentelemetry-go#7325

[svrnm]

based on the comment & issue description this is accepted and ready to be implemented, I assumed you as sponsor @pellared