Clarify server.address | port on RPC server, use recommended requirement level on server spans and opt-in on server metric

[lmolkova]

Fixes #3784

Changes

Align server.address | port with HTTP server

• address is recommended (when available) on server spans and opt-in on metrics (due to possible high-cardinality and limited value)
• we document how to populate it on grpc

Add section to gRPC server that it comes from :authority (not always exposed in public APIs - c++, java, .net.

Given it's exposed as public API, it seems to have enough significance to be captured on telemetry.

Merge requirement checklist

• CONTRIBUTING.md guidelines followed.
• Links to prototypes or existing instrumentations (when adding or changing conventions)
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[Copilot]

Pull request overview

This PR updates the RPC semantic conventions to better align server.address / server.port on RPC server spans with the HTTP server guidance, including documenting how to populate these attributes for gRPC.

Changes:

• Updates the RPC model to recommend server.address on server spans (when available) and adds gRPC-specific population guidance based on HTTP/2 authority information.
• Adjusts RPC and gRPC documentation to reflect the updated requirement levels and guidance for server.address / server.port.
• Reorders/renumbers the affected attribute table rows and footnotes to match the updated model.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
model/rpc/spans.yaml	Adds/updates server.address/server.port guidance for generic RPC server spans and gRPC server spans.
docs/rpc/rpc-spans.md	Updates the rendered RPC server span attribute table and footnotes to reflect the new model guidance.
docs/rpc/grpc.md	Updates the rendered gRPC server span attribute table and footnotes to reflect the new model guidance.

Comments suppressed due to low confidence (1)

model/rpc/spans.yaml:280

• To align with the HTTP server conventions, server.port on gRPC server spans should remain conditionally required when available (and only when server.address is set), rather than merely recommended. Relaxing this requirement makes gRPC inconsistent with the general server.port guidance and with the stated goal of aligning with HTTP server semantics.

        requirement_level:
          recommended: If `server.address` is set.