Config: Make LoggerConfig `additive` flag default true

[mkykadir]

This is more intuitive and easies the configuration process.

Fixes #3295

Perhaps the default should be additive so that it behaves as expected.

Originally posted by @hewison-chris in https://github.com/bosagora/agora/issues/3295#issuecomment-1099822597

[codecov[bot]]

Codecov Report

Merging #3302 (35b4430) into v0.x.x (c60c869) will decrease coverage by 0.35%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           v0.x.x    #3302      +/-   ##
==========================================
- Coverage   88.15%   87.79%   -0.36%     
==========================================
  Files         165      164       -1     
  Lines       17067    16964     -103     
==========================================
- Hits        15045    14894     -151     
- Misses       2022     2070      +48     

Flag	Coverage Δ
integration	?
unittests	87.79% <ø> (+0.01%)	:arrow_up:

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

Impacted Files	Coverage Δ
source/agora/utils/Log.d	57.23% <ø> (-5.04%)	:arrow_down:
source/agora/node/Runner.d	0.00% <0.00%> (-40.53%)	:arrow_down:
source/scpd/types/Stellar_SCP.d	68.99% <0.00%> (-30.24%)	:arrow_down:
source/agora/node/Validator.d	90.90% <0.00%> (-0.55%)	:arrow_down:
source/agora/script/Engine.d	97.34% <0.00%> (-0.15%)	:arrow_down:
source/agora/node/main.d
source/agora/consensus/protocol/Nominator.d	91.65% <0.00%> (+0.17%)	:arrow_up:
source/agora/test/Base.d	80.70% <0.00%> (+0.22%)	:arrow_up:
source/agora/test/ValidatorRecurringEnrollment.d	95.19% <0.00%> (+0.96%)	:arrow_up:
... and 1 more

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