[nis]: add additional block info to /local/block/at

[Jaguar0625]

problem: cannot determine block beneficiary directly
solution: add 'beneficiary' and 'totalFee' to result from /local/block/at

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.51%. Comparing base (67de650) to head (b60b352).
Report is 1 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff            @@
##                dev     #538   +/-   ##
=========================================
  Coverage     93.51%   93.51%           
- Complexity     5981     5982    +1     
=========================================
  Files           709      709           
  Lines         17086    17088    +2     
  Branches       1278     1279    +1     
=========================================
+ Hits          15978    15980    +2     
  Misses          862      862           
  Partials        246      246           

Flag	Coverage Δ
gocrypto	77.04% <ø> (ø)
nem-core	95.51% <ø> (ø)
nem-deploy	52.98% <ø> (ø)
nem-nis	94.11% <100.00%> (+<0.01%)	⬆️
nem-peer	94.11% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
.../controller/viewmodels/ExplorerBlockViewModel.java	100.00% <100.00%> (ø)

[Wayonb]

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