API: add OnlineCirculation to GetSupply

[cce]

Summary

The online circulation used by agreement (which excludes online accounts that have expired, but haven't been marked offline) is implemented in Ledger.OnlineCirculation but not exposed to the REST API. This adds it to GetSupply and SupplyResponse.

Test Plan

Updated TestGetSupply

[codecov]

Codecov Report

Attention: Patch coverage is 57.89474% with 16 lines in your changes missing coverage. Please review.

Project coverage is 51.86%. Comparing base (005bf7e) to head (cdec276).
Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
daemon/algod/api/server/v2/handlers.go	0.00%	14 Missing ⚠️
daemon/algod/api/server/v2/test/helpers.go	91.66%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6322   +/-   ##
=======================================
  Coverage   51.85%   51.86%           
=======================================
  Files         652      652           
  Lines       87433    87462   +29     
=======================================
+ Hits        45340    45358   +18     
- Misses      39226    39239   +13     
+ Partials     2867     2865    -2     

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[algorandskiy]

maybe add some clarification about the value: like not a value at the moment but at -320 rounds back as consensus defines? Or it is too much?

[cce]

Oh that is a good point, I could add something about how this is the balance at current-320 used to vote on the current-round field