Migrate semantic conventions code generation to Weaver

[rogercoll]

Is your feature request related to a problem? Please describe.

semconvgen tool fails at generating Semantic conventions packages for version > v1.27.0:

$ make gensemconv SPECPATH=/tmp/opentelemetry/semantic-conventions SPECTAG=v1.29.0
...
          File "/usr/local/lib/python3.13/site-packages/opentelemetry/semconv/model/utils.py", line 97, in raise_or_warn
            raise error
        opentelemetry.semconv.model.exceptions.ValidationError: Semantic Convention metric.container.network.io reference `network.interface.name` but it cannot be found! - @73:5 ('metric.container.network.io')


goroutine 1 [running]:
main.main()
        go.opentelemetry.io/build-tools/[email protected]/generator.go:64 +0x665
make: *** [Makefile:251: gensemconv] Error 2

Describe the solution you'd like

As no new version will be produced for build-tools, the maintained OpenTelemetry Weaver tool should be used. See:

• Announcement: sunsetting semantic conventions build tooling build-tools#322
• https://github.com/open-telemetry/semantic-conventions/blob/main/docs/non-normative/code-generation.md#generating-semantic-conventions