Connect async storage with async instruments

[lalitb]

Fixes #1387

Changes

While we do support creating async storage separately, it needs to be connected to the async instruments.
Also added it in the ostream exporter example.

For significant contributions please make sure you have completed the following items:

• CHANGELOG.md updated for non-trivial changes
• Unit tests have been added
• Changes in public API reviewed

[codecov]

Codecov Report

Merging #1388 (ea3aa3b) into main (3fd5ca3) will decrease coverage by 0.10%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main    #1388      +/-   ##
==========================================
- Coverage   85.51%   85.41%   -0.09%     
==========================================
  Files         151      152       +1     
  Lines        4318     4344      +26     
==========================================
+ Hits         3692     3710      +18     
- Misses        626      634       +8     

Impacted Files	Coverage Δ
api/include/opentelemetry/metrics/meter.h	100.00% <ø> (ø)
api/include/opentelemetry/metrics/noop.h	39.14% <0.00%> (+4.52%)	⬆️
sdk/include/opentelemetry/sdk/metrics/meter.h	0.00% <0.00%> (ø)
sdk/src/metrics/meter.cc	6.25% <0.00%> (-1.44%)	⬇️
sdk/src/metrics/metric_reader.cc	63.89% <0.00%> (+8.34%)	⬆️
...metrics/export/periodic_exporting_metric_reader.cc	77.28% <0.00%> (+34.10%)	⬆️

[marcalff]

In RegisterAsyncMetricStorage(), do we need something similar to RegisterMetricStorage:

    auto view_instr_desc = instrument_descriptor;
    if (!view.GetName().empty())
    {
      view_instr_desc.name_ = view.GetName();
    }
    if (!view.GetDescription().empty())
    {
      view_instr_desc.description_ = view.GetDescription();
    }

For empty view names and description, the metric exported should use the name and description of the underlying instrument.