pika: add opt-in `messaging.rabbitmq.cluster.name` / `messaging.rabbitmq.vhost.name` span attributes

What problem do you want to solve?

opentelemetry-instrumentation-pika has no way to surface which RabbitMQ vhost or cluster
a message was published to/consumed from. This matters for anyone running multiple vhosts
on a shared broker (multi-tenant) or multiple clusters — without it, traces from different
logical RabbitMQ environments are indistinguishable. These aren't official
semantic-conventions attributes yet (tracked upstream in open-telemetry/semantic-conventions#3997),
so nothing standard covers this today.

Describe the solution you'd like

Add two span attributes, populated from data pika already has on the Connection object:

• messaging.rabbitmq.vhost.name ← connection.params.virtual_host
• messaging.rabbitmq.cluster.name ← connection.server_properties.get("cluster_name")

Since neither is a stable spec attribute, and not every user wants the extra cardinality,
gate each independently behind its own boolean env var, off by default:

• OTEL_PYTHON_PIKA_CAPTURE_VHOST_NAME
• OTEL_PYTHON_PIKA_CAPTURE_CLUSTER_NAME

Parsed the same way as other OTEL_PYTHON_* boolean flags in this repo (e.g.
OTEL_PYTHON_LOG_CODE_ATTRIBUTES): "true" (case-insensitive, trimmed) = enabled,
anything else = disabled. Two independent flags rather than one combined flag, so a user
who only cares about one doesn't pay for the other.

Describe alternatives you've considered

There isn't much room for alternatives to the feature

Additional Context

No response

Would you like to implement a fix?

Yes

Tip

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Start by locating the opentelemetry-instrumentation-pika span creation and the existing OTEL_PYTHON_* boolean flag parsing, then inspect how the pika Connection exposes virtual_host and cluster_name. Add independently gated attributes and verify spans with each flag enabled and disabled, including the requested true parsing behavior.