Metrics supplemental guidelines for async views

[jmacd]

Fixes #2187

Changes

Clarifies the available strategies for calculating asynchronous Views and what it means for the receiver, especially when streams "die" and restart, requiring reset detection.

Related issues #1874

[jsuereth]

This looks great to me. I think it nails options available to SDKs and provides a simple, allowable implementation, demonstrating why it works.

Should we recommend ONE option to SDKs first though, while allowing the others?

[pirgeo]

Thanks for the clarification! I wonder: for the Synchronous example, there are the Delta, then the Cumulative aggregation temporality sections, but for Asynchronous there is the Cumulative section first, then the Delta section. In the attribute removal section right after that, there are references to Cumulative temporality again. Do you think it would make sense to swap the Delta and Cumulative sections for the Asynchronous example?

[jmacd]

@pirgeo to rationalize the differently-ordered temporality sections for sync vs async, 8556ff6.

[github-actions]

This PR was marked stale due to lack of activity. It will be closed in 7 days.

[legendecas]

👍

[github-actions]

Closed as inactive. Feel free to reopen if this PR is still being worked on.

[carlosalberto]

@jmacd Should we reopen this PR? It had a few approvals already, etc ;)

[jmacd]

Given that these are guidelines--not specs--and have several approvals, I feel this can merge. @reyang PTAL.

[reyang]

LGTM.