feat: add WSGI adapter

[WilliamBergamin]

This PR introduced a WSGI adapter to bolt python, this will allow Bolt to be deployed in production without the need for an other WSGI compatible Web Framework like Flask

Testing

1. Pull this branch
2. Use the examples/wsgi/app.py as starting point for a test app
3. Run scripts/build_pypi_package.sh
4. Use the .whl file found under dist/ to run pip install /path/to/dist/slack_bolt.whl
5. Run pip install gunicorn
6. Run gunicorn app:api -b 0.0.0.0:3000 --log-level debug to start the application

Category

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

Requirements

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

• [x] I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• [x] I've read and agree to the Code of Conduct.
• [x] I've run ./scripts/install_all_and_run_tests.sh after making the changes.

[seratch]

Can you check the flake8 errors? https://github.com/slackapi/bolt-python/actions/runs/9228875341/job/25393855815?pr=1085

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 91.95402% with 7 lines in your changes are missing coverage. Please review.

Project coverage is 91.76%. Comparing base (dbe2333) to head (dd719c0).

Files	Patch %	Lines
slack_bolt/adapter/wsgi/handler.py	84.61%	6 Missing :warning:
slack_bolt/adapter/wsgi/http_response.py	95.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1085 +/- ## ======================================= Coverage 91.76% 91.76% ======================================= Files 181 186 +5 Lines 6315 6403 +88 ======================================= + Hits 5795 5876 +81 - Misses 520 527 +7 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.