[Metrics SDK] Histogram min/max support

[lalitb]

It seems Explicit bucket histogram aggregation should support the optional required configuration for min/max support. This is something missing in the current implementation.

https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/metrics/sdk.md#explicit-bucket-histogram-aggregation

The summary of changes required:

• adds min/max recording to Histograms
• makes this configurable via the Aggregation
• Update proto to 0.18.0 to make it exportable.

Depends on #1444 - should be possible to configure min/max using configuration

[lalitb]

@esigo - Do you want me to pick this issue, unless you have already started on it :) I would have some bandwidth this week, so checking.

ok please ignore the above. I will work on #1339 first. Looks like, that would take a couple of days. Can take this after that in case you want me to :)