Make all aggregated counts in views optional

[pfrazee]

• Affects profile view and post view
• Reasoning:
  • There may be cases where view providers are unable or not designed to surface this information. Rather than give an incorrect count (ie “0”) they should give undefined. Client UIs should handle this by not showing the information.

[dholms]

fixed https://github.com/bluesky-social/atproto/pull/658