Provide versioned semantic conventions with sub-package/folder

The idea is to create a new folder for each version of semantic conventions release and instrumentation packages or end users can choose which one to use.

The folder structure will look like following

opentelemetry-semantic-conventions/src/opentelemetry/semconv
  /v1_13_0
    /trace
    /resource
    /metric
    /..
  /v1_12_0
  /v1_11_0

It is convenient to use this because we don't necessarily need to update the instrumentation every time there is a spec release. This will enable us to mark the package as stable since there will always be a backward compatible sub-package but the downside is it can grow big over time. The current size of the package seems to be around 26kb https://pypi.org/project/opentelemetry-semantic-conventions/#files. Original inspiration from go SKD https://github.com/open-telemetry/opentelemetry-go/tree/main/semconv

Start by reviewing the proposed opentelemetry-semantic-conventions/src/opentelemetry/semconv layout and the referenced OpenTelemetry Go semconv structure. Clarify how released versions should map to trace, resource, and metric sub-packages, and how instrumentation or end users select them. Done means multiple semantic-convention versions can coexist while preserving backward-compatible access.