netgoal: Use --last-part-key-round when generating a goalnet template

[nullun]

Whenever I've generated a goalnet template using netgoal I have to manually modify the LastPartKeyRound value from 3000000 to something like 10000, depsite using the --last-part-key-round argument in the command.
Example:

netgoal generate -n 1 -R 0 -w 4 --last-part-key-round 10000 -t goalnet -r tmpnet -o tmpnet.json
goal network create -t tmpnet.json -n tmpnet --start -r tmpnet

This fix works in the same way generating a genesis template works. I've no idea how many people use this, but it's a nice quick QOL update for me.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (877090b) 55.99% compared to head (4b54c45) 55.97%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5912      +/-   ##
==========================================
- Coverage   55.99%   55.97%   -0.03%     
==========================================
  Files         478      478              
  Lines       67602    67602              
==========================================
- Hits        37855    37838      -17     
- Misses      27187    27200      +13     
- Partials     2560     2564       +4     

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[jannotti]

Seems reasonable to me