netdeploy: Add override to enable devmode for a network template.

[winder]

Summary

Thinking out loud a little bit with this PR.

Rather than requiring a separate network configuration, this flag lets you run an existing single node network template in dev mode. This would allow tools like sandbox to ship with a single template instead of two.

Test Plan

Ran manually with OneNodeFuture.json template.

[codecov-commenter]

Codecov Report

Merging #3904 (8b2042c) into master (12ded27) will decrease coverage by 0.02%.
The diff coverage is 12.50%.

@@            Coverage Diff             @@
##           master    #3904      +/-   ##
==========================================
- Coverage   50.09%   50.06%   -0.03%     
==========================================
  Files         394      394              
  Lines       68456    68463       +7     
==========================================
- Hits        34294    34278      -16     
- Misses      30465    30476      +11     
- Partials     3697     3709      +12     

Impacted Files	Coverage Δ
netdeploy/network.go	8.92% <0.00%> (-0.18%)	⬇️
netdeploy/networkTemplate.go	30.90% <0.00%> (-0.58%)	⬇️
cmd/goal/network.go	17.39% <50.00%> (+0.90%)	⬆️
network/wsPeer.go	65.83% <0.00%> (-5.84%)	⬇️
crypto/merkletrie/trie.go	66.42% <0.00%> (-2.19%)	⬇️
crypto/merkletrie/node.go	91.62% <0.00%> (-1.87%)	⬇️
catchup/service.go	68.88% <0.00%> (-0.75%)	⬇️
data/transactions/verify/txn.go	45.02% <0.00%> (+0.86%)	⬆️
node/node.go	25.03% <0.00%> (+1.84%)	⬆️

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[cce]

seems straightforward