[v2] Fix #405 by providing a better way to configure logger

[seratch]

Summary

This pull request brings the changes by #406 (fixes #405) to the v2 branch.

Requirements (place an x in each [ ])

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

[codecov]

Codecov Report

Merging #413 into @slack/bolt@next will increase coverage by 0.14%.
The diff coverage is n/a.

@@                 Coverage Diff                  @@
##           @slack/bolt@next     #413      +/-   ##
====================================================
+ Coverage             85.37%   85.51%   +0.14%     
====================================================
  Files                     7        7              
  Lines                   506      511       +5     
  Branches                144      146       +2     
====================================================
+ Hits                    432      437       +5     
  Misses                   49       49              
  Partials                 25       25              

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