Fix #738 Add more keyword args to say utility

[seratch]

This pull request resolves #738

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 #741 (2d6fe0d) into main (4f1b4f8) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head 2d6fe0d differs from pull request most recent head 42c05c4. Consider uploading reports for the commit 42c05c4 to get more accurate results

@@           Coverage Diff           @@
##             main     #741   +/-   ##
=======================================
  Coverage   92.06%   92.06%           
=======================================
  Files         172      172           
  Lines        5873     5875    +2     
=======================================
+ Hits         5407     5409    +2     
  Misses        466      466           

Impacted Files	Coverage Δ
slack_bolt/context/say/async_say.py	96.29% <100.00%> (+0.14%)	⬆️
slack_bolt/context/say/say.py	96.29% <100.00%> (+0.14%)	⬆️

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more