SemConv metrics codegen: include histogram boundaries

[lmolkova]

See open-telemetry/opentelemetry-python-contrib#3891

We can't use metrics helpers since they don't configure histogram boundaries. E.g.

opentelemetry-python/opentelemetry-semantic-conventions/src/opentelemetry/semconv/_incubating/metrics/gen_ai_metrics.py

Lines 28 to 34 in e0ac0a4

	def create_gen_ai_client_operation_duration(meter: Meter) -> Histogram:
	"""GenAI operation duration"""
	return meter.create_histogram(
	name=GEN_AI_CLIENT_OPERATION_DURATION,
	description="GenAI operation duration.",
	unit="s",
	)

Blocked on open-telemetry/semantic-conventions#1225 - semconv yaml does not include boundaries and we can't generate corresponding code.