[BUG] `gen_ai.agent.name` OTel attribute used for MultiAgent spans even when an "agent" may not be used

[dbschmigelski]

Problem Statement

The start_multiagent_span adds an attribute

{
    "gen_ai.agent.name": instance,
}

For Swarm we set this to "swarm", this may make sense, but for Graph, setting this to "graph" does not seem to make sense. In #991 we followed the same pattern, setting the gen_ai.agent.name to "function_node" which again doesn't seem to make sense since it does not represent an agent.

There is likely a more appropriate attribute, like gen_ai.operation.name, which should be used instead.

Proposed Solution

No response

Use Case

Users inspecting traces should easily differentiate spans for a Strands Agent and a MultiAgent which does not necessarily represent an "Agent"

Alternatives Solutions

No response

Additional Context

No response