[otlpexporter] Validate endpoint has port

[atoulme]

trafficstars

2024-02-07T02:18:55.694Z	error	exporterhelper/queue_sender.go:123	Exporting failed. No more retries left. Dropping data.	{"kind": "exporter", "data_type": "traces", "name": "otlp/XXX", "error": "rpc error: code = Unavailable desc = connection error: desc = \"transport: Error while dialing: dial tcp: address example.com: missing port in address\"", "dropped_items": 335}
go.opentelemetry.io/collector/exporter/exporterhelper.(*queueSender).consume
	go.opentelemetry.io/collector/[email protected]/exporterhelper/queue_sender.go:123
go.opentelemetry.io/collector/exporter/exporterhelper/internal.(*boundedMemoryQueue[...]).Consume
	go.opentelemetry.io/collector/[email protected]/exporterhelper/internal/bounded_memory_queue.go:55
go.opentelemetry.io/collector/exporter/exporterhelper/internal.(*QueueConsumers[...]).Start.func1
	go.opentelemetry.io/collector/[email protected]/exporterhelper/internal/consumers.go:43

If you omit the port from the endpoint used by the otlp exporter, it starts ok but fails to run with an error. Instead, we should have a default port or validate the endpoint on start.