fix: correct indentation for json config for better readability

[woile]

Description

Output the json config as multi line instead of single-line.
This is much more readable.

Checklist

• Run ./script/format and ./script/test locally to ensure this change passes linter check and test
• Test the changes on the local machine manually

Expected behavior

Output should look like this:

{
  "commitizen": {
    "name": "cz_conventional_commits",
    "version": "0.0.1",
    "tag_format": "$version"
  }
}

[codecov]

Codecov Report

Merging #394 (986f2d8) into master (00f81d3) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #394   +/-   ##
=======================================
  Coverage   97.90%   97.90%           
=======================================
  Files          39       39           
  Lines        1381     1381           
=======================================
  Hits         1352     1352           
  Misses         29       29           

Flag	Coverage Δ
unittests	97.90% <100.00%> (ø)

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Impacted Files	Coverage Δ
commitizen/__version__.py	100.00% <100.00%> (ø)
commitizen/config/json_config.py	100.00% <100.00%> (ø)

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