config: fix the default value of log.format

[JmPotato]

Signed-off-by: JmPotato ghzpotato@gmail.com

What problem does this PR solve?

Issue Number: Close #4753

#4532 removed the code to initialize the default value of log.format. This PR adds it back.

What is changed and how it works?

config: fix the default value of log.format

Check List

Tests

• Unit test
• Integration test

Release note

None.

[ti-chi-bot]

[REVIEW NOTIFICATION]

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• nolouch

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[codecov]

Codecov Report

Merging #4754 (a5d07e5) into master (d58d7c9) will decrease coverage by 0.10%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #4754      +/-   ##
==========================================
- Coverage   75.23%   75.12%   -0.11%     
==========================================
  Files         287      287              
  Lines       28161    28163       +2     
==========================================
- Hits        21186    21158      -28     
- Misses       5108     5134      +26     
- Partials     1867     1871       +4     

Flag	Coverage Δ
unittests	75.12% <100.00%> (-0.11%)	⬇️

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

Impacted Files	Coverage Δ
server/config/config.go	78.03% <100.00%> (+0.09%)	⬆️
server/election/leadership.go	73.19% <0.00%> (-7.22%)	⬇️
server/tso/local_allocator.go	64.86% <0.00%> (-6.76%)	⬇️
server/tso/allocator_manager.go	63.45% <0.00%> (-3.93%)	⬇️
server/tso/tso.go	66.85% <0.00%> (-2.86%)	⬇️
pkg/etcdutil/etcdutil.go	85.88% <0.00%> (-2.36%)	⬇️
server/member/member.go	63.10% <0.00%> (-1.61%)	⬇️
server/region_syncer/client.go	83.59% <0.00%> (-1.57%)	⬇️
server/schedule/operator_controller.go	84.44% <0.00%> (-1.22%)	⬇️
server/storage/hot_region_storage.go	78.73% <0.00%> (-1.15%)	⬇️
... and 10 more

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[nolouch]

lgtm

[nolouch]

/merge

[ti-chi-bot]

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/run-all-tests

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[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: a5d07e5

[ti-chi-bot]

In response to a cherrypick label: new pull request created: #4755.