Merge rpc.method and rpc.service into fully-qualified rpc.method, clarify span name and possible high cardinality

[lmolkova]

Fixes #3196, fixes #2863

• Deprecate rpc.method and rpc.service in favor of new rpc.method.name
• Add note on restricting that new attribute to recognized methods (similarly to http.request.method)
• Introduce rpc.method.name_original similarly to http.request.method_original
• Update span name section to use new attribute

[Copilot]

Pull request overview

This pull request refactors RPC semantic conventions by merging the previously separate rpc.method and rpc.service attributes into a single fully-qualified rpc.method.name attribute (e.g., com.example.ExampleService/exampleMethod). This change addresses issues #2863 and #3196 by simplifying the attribute model while providing clear guidance on handling potentially unbounded cardinality through a standardized _OTHER mechanism similar to HTTP conventions.

Key Changes

• Attribute consolidation: Merged rpc.method and rpc.service into rpc.method.name containing the fully-qualified method name
• Cardinality control: Introduced rpc.method.name_original and _OTHER sentinel value to handle unrecognized methods that could cause cardinality explosions
• Updated span naming: Clarified that span names should use {rpc.method.name} when available and not _OTHER, otherwise fall back to {rpc.system.name}

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
model/rpc/registry.yaml	Defined new rpc.method.name and rpc.method.name_original attributes with detailed cardinality guidance
model/rpc/deprecated/registry-deprecated.yaml	Deprecated rpc.method and rpc.service with migration guidance
model/rpc/spans.yaml	Updated all RPC span definitions to use new attributes; removed obsolete rpc_service.server group
model/rpc/metrics.yaml	Updated RPC metrics to reference rpc.method.name instead of deprecated attributes
model/rpc/common.yaml	Updated common RPC attributes to reference new attribute names
docs/rpc/rpc-spans.md	Rewrote span naming section and updated all attribute tables with new attributes and cardinality notes
docs/rpc/rpc-metrics.md	Updated all metric attribute tables to use rpc.method.name
docs/rpc/grpc.md	Updated gRPC-specific conventions with new attributes and detailed cardinality guidance
docs/rpc/connect-rpc.md	Updated Connect RPC conventions with new attributes
docs/rpc/json-rpc.md	Updated JSON-RPC conventions with specific opt-in guidance due to protocol's unbounded method names
docs/registry/attributes/rpc.md	Updated attribute registry documentation with new definitions and deprecated old attributes
docs/object-stores/s3.md	Marked deprecated rpc.method and rpc.service attributes
docs/db/dynamodb.md	Marked deprecated rpc.method and rpc.service attributes in all DynamoDB operation tables
docs/cloud-providers/aws-sdk.md	Marked deprecated rpc.method and rpc.service attributes
.chloggen/rpc-method-service.yaml	Added changelog entry documenting the breaking change