Add `additive` field to the TestNet configuration

[linked0]

There was no log message while running a validator on TestNet. It was because the additive field was missing in the logging config of a configuration file.

[codecov[bot]]

Codecov Report

Merging #3267 (e5daeff) into v0.x.x (8a3efd7) will decrease coverage by 0.21%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           v0.x.x    #3267      +/-   ##
==========================================
- Coverage   87.81%   87.59%   -0.22%     
==========================================
  Files         164      164              
  Lines       16923    16923              
==========================================
- Hits        14861    14824      -37     
- Misses       2062     2099      +37     

Flag	Coverage Δ
integration	36.16% <ø> (?)
unittests	87.54% <ø> (-0.27%)	:arrow_down:

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

Impacted Files	Coverage Δ
source/agora/consensus/BlockStorage.d	68.90% <0.00%> (-10.61%)	:arrow_down:
source/agora/node/FullNode.d	72.13% <0.00%> (-1.24%)	:arrow_down:
source/agora/consensus/protocol/Nominator.d	91.10% <0.00%> (-0.89%)	:arrow_down:
source/agora/common/BanManager.d	86.55% <0.00%> (-0.85%)	:arrow_down:
source/agora/consensus/state/Ledger.d	89.93% <0.00%> (-0.68%)	:arrow_down:
source/agora/node/Validator.d	90.90% <0.00%> (-0.51%)	:arrow_down:
source/agora/network/Manager.d	78.36% <0.00%> (-0.33%)	:arrow_down:
source/agora/test/Flash.d	95.12% <0.00%> (-0.11%)	:arrow_down:
source/agora/utils/Log.d	62.26% <0.00%> (+5.03%)	:arrow_up:

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