Update "OSS Expectations" (#6551)

## What are you changing in this pull request and why?

Follow-up to:
- #5584
- https://www.youtube.com/watch?v=DC9sbZBYzpI
- https://www.youtube.com/watch?v=I72yUtrmhbY

Let's make sure our public expectations are aligned with our teams'
commitments around responding to OSS discussions/issues and reviewing
externally contributed PRs

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Co-authored-by: graciegoheen <[email protected]>
Co-authored-by: Doug Beatty <[email protected]>
Co-authored-by: Matt Shaver <[email protected]>