Add ability to output logs in JSON format

[croemmich]

Description

Adds the ability to use the Logrus JSONFormatter.

Motivation and Context

Allows for simple end-to-end structured logging via Docker -> Fluentd -> ElasticSearch.

How Has This Been Tested?

Tested manually. Ensured new and default behavior.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov-io]

Codecov Report

Merging #253 into master will decrease coverage by 0.18%.
The diff coverage is 42.85%.

@@           Coverage Diff            @@
##           master   #253      +/-   ##
========================================
- Coverage   82.18%    82%   -0.19%     
========================================
  Files          26     26              
  Lines        1521   1528       +7     
========================================
+ Hits         1250   1253       +3     
- Misses        203    207       +4     
  Partials       68     68

Impacted Files	Coverage Δ
pkg/config/config.go	79.1% <42.85%> (-4.23%)	⬇️

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[zhouzhuojie]

LGTM. Left one comment