Use byte format for asset b64 fields

[winder]

Summary

While adding Indexer support for these, I realized that for a model object we can specify byte formatting. The HTTP responses won't change with this change, so this isn't strictly required for the release.

Test Plan

e2e sub test

[tsachiherman]

looks good to me, although it's a bit confusing since I can't really see the base64 encoder in action.

[winder]

There are calls like ctx.JSON(http.StatusOK, response) which do encoding with the echo framework for most endpoints

[codecov-commenter]

Codecov Report

Merging #2573 (63442f8) into master (3069c69) will increase coverage by 0.01%.
The diff coverage is 20.00%.

@@            Coverage Diff             @@
##           master    #2573      +/-   ##
==========================================
+ Coverage   46.86%   46.87%   +0.01%     
==========================================
  Files         346      346              
  Lines       55668    55663       -5     
==========================================
+ Hits        26088    26094       +6     
+ Misses      26624    26614      -10     
+ Partials     2956     2955       -1     

Impacted Files	Coverage Δ
libgoal/libgoal.go	3.08% <0.00%> (+0.03%)	⬆️
daemon/algod/api/server/v2/account.go	76.12% <100.00%> (ø)
ledger/catchpointwriter.go	68.18% <0.00%> (-1.30%)	⬇️
network/requestTracker.go	71.12% <0.00%> (-0.44%)	⬇️
ledger/blockqueue.go	81.03% <0.00%> (ø)
network/wsNetwork.go	60.73% <0.00%> (ø)
cmd/algoh/blockWatcher.go	77.77% <0.00%> (ø)
ledger/eval.go	76.68% <0.00%> (+0.29%)	⬆️
ledger/acctupdates.go	62.25% <0.00%> (+0.33%)	⬆️
daemon/algod/api/server/v2/utils.go	16.81% <0.00%> (+2.65%)	⬆️

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