Remove network.type from RPC spans and metrics

[Copilot]

• Remove network.type from RPC attribute groups in model/rpc/common.yaml
  • Remove from rpc attribute group (line 49)
  • Remove from rpc.server attribute group (line 88)
  • Remove from rpc_service.server attribute group (line 102)
• Run table-check to verify YAML changes are valid
• Run table-generation to regenerate documentation from YAML
• Run all validation checks (schema-check, misspell, markdownlint, etc.)
• Verify the generated documentation no longer contains network.type references
• Add changelog entry

Summary

Successfully removed network.type attribute from all RPC spans and metrics following the same pattern used in PR #410 for HTTP. The attribute is still available in the registry for opt-in usage but is no longer included in RPC semantic conventions as a recommended attribute.

Changes made:

• Removed 3 references to network.type from model/rpc/common.yaml
• Regenerated documentation files: docs/rpc/rpc-spans.md, docs/rpc/connect-rpc.md, docs/rpc/json-rpc.md
• Added changelog entry at .chloggen/2851.yaml
• Net reduction: -102 lines (attribute references and footnotes removed)

All validation checks pass:
✅ table-check
✅ schema-check
✅ misspell
✅ markdownlint
✅ chlog-validate

Original prompt

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This section details on the original issue you should resolve

<issue_title>Remove network.type from RPC spans / metrics</issue_title>
<issue_description>We've removed it from HTTP - #410 with the motivation that it's not really interesting in a common case and, being in the registry, it's already can be considered opt-in.

Suggesting to remove from RPC following the same motivation</issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #2851

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[thompson-tomo]

@trask this will need a rebase now that grpc doc has been merged