collect doesn't return anything, so returning True until we implement timeout/error handling mechanism seemed reasonable to me. What do you think?

Originally posted by @lonewolf3739 in #2401 (comment)

Also, the timeout mechanism is required in several parts of the metrics spec:

1. MeterProvider.shutdown
2. MeterProvider.forceflush
3. Asynchronous callbacks
4. MetricReader.collect
5. MetricReader.shutdown
6. PushMetricExporter.forceflush
7. PushMetricExporter.shutdown