Add prototype support for bound instruments to the metrics API

[martincostello]

See open-telemetry/opentelemetry-specification#4126 for more details about Bound Instruments.

From open-telemetry/opentelemetry-specification#5050 (comment):

I think OTel .NET Sdk can now do a prototype without needing any change from (.NET) runtime

[martincostello]

This issue is tracking implementation for .NET, not Erlang.

[ashwathranjol]

I'm interested in contributing to this.