netgoal: start with at least 20GB RootStorage

[algolucky]

Summary

• bumps the constant when calculating required storage for instances using netgoal to 20
  • for instance, with a single NPN and no relays, the return value changes from 20 to 30
  • this was highlighted when spinning up mainnet NPNs and running fast-catchup, the data directories are approaching, if not exceeding, 20GB

Test Plan

• load generator pipeline

[codecov]

Codecov Report

Merging #4779 (7e8aaca) into master (995ae47) will increase coverage by 0.01%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #4779      +/-   ##
==========================================
+ Coverage   54.59%   54.61%   +0.01%     
==========================================
  Files         414      414              
  Lines       53517    53517              
==========================================
+ Hits        29219    29226       +7     
+ Misses      21878    21868      -10     
- Partials     2420     2423       +3     

Impacted Files	Coverage Δ
netdeploy/remote/deployedNetwork.go	19.77% <0.00%> (ø)
data/transactions/verify/txn.go	76.19% <0.00%> (-0.96%)	⬇️
ledger/testing/randomAccounts.go	56.61% <0.00%> (-0.62%)	⬇️
ledger/acctonline.go	78.12% <0.00%> (-0.53%)	⬇️
catchup/service.go	68.14% <0.00%> (-0.50%)	⬇️
ledger/accountdb.go	72.55% <0.00%> (-0.16%)	⬇️
ledger/tracker.go	74.89% <0.00%> (ø)
network/wsNetwork.go	65.80% <0.00%> (+0.46%)	⬆️
cmd/tealdbg/debugger.go	73.49% <0.00%> (+0.80%)	⬆️
catchup/peerSelector.go	100.00% <0.00%> (+1.04%)	⬆️
... and 2 more

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