Support incubating semconv stability levels

[dl-alexandre]

Summary

• treat the generated incubating semantic-convention pass as "all non-stable" instead of matching only experimental
• update Elixir and Erlang semconv templates so incubating output still uses incubating namespaces/includes for development, rc, and experimental stability levels
• keep stable generation as an exact stable match

Fixes #823.

Validation

• ruby -e 'require "yaml"; YAML.load_file("apps/opentelemetry_semantic_conventions/templates/registry/elixir/weaver.yaml"); YAML.load_file("apps/opentelemetry_semantic_conventions/templates/registry/erlang/weaver.yaml")'
• jq -n --arg stability stable '[{stability:"stable"},{stability:"development"},{stability:"rc"},{stability:"experimental"}] | map(select(($stability == "stable" and .stability == "stable") or ($stability != "stable" and .stability != "stable")))'
• jq -n --arg stability incubating '[{stability:"stable"},{stability:"development"},{stability:"rc"},{stability:"experimental"}] | map(select(($stability == "stable" and .stability == "stable") or ($stability != "stable" and .stability != "stable")))'
• git diff --check
• mix deps.get
• mix test
• mix format --check-formatted

Note: I did not regenerate semantic-convention output in this branch; this changes the generator filters/templates only.

[linux-foundation-easycla]

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