Fix #430 by adding a new option to customize dev server (http.server) logging

[seratch]

This pull request fixes #430 by adding a new option http_server_logger_enabled to customize (disable) dev server's default logging, which is not configurable via the standard logging module (as the log_message function writes stderr anyway).

Developers can change the http_server_logger_enabled value in App#start() method arguments. The default value is True.

from slack_bolt import App
app = App()

if __name__ == "__main__":
    app.start(3000, http_server_logger_enabled=False)

AsyncApp runs the AIOHTTP web server, which works with logging module. Thus, we don't need to add the same option to it.

Category (place an x in each of the [ ])

• slack_bolt.App and/or its core components
• slack_bolt.async_app.AsyncApp and/or its core components
• Adapters in slack_bolt.adapter
• Document pages under /docs
• Others

Requirements (place an x in each [ ])

Please read the Contributing guidelines and Code of Conduct before creating this issue or pull request. By submitting, you are agreeing to those rules.

• 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.
• I've run ./scripts/install_all_and_run_tests.sh after making the changes.

[codecov]

Codecov Report

Merging #431 (b7a7c00) into main (0692846) will decrease coverage by 0.02%.
The diff coverage is 71.42%.

@@            Coverage Diff             @@
##             main     #431      +/-   ##
==========================================
- Coverage   91.36%   91.33%   -0.03%     
==========================================
  Files         167      167              
  Lines        5491     5496       +5     
==========================================
+ Hits         5017     5020       +3     
- Misses        474      476       +2     

Impacted Files	Coverage Δ
slack_bolt/app/app.py	87.55% <71.42%> (-0.32%)	⬇️

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[seratch]

Thanks for the quick review!