docs: updates for agent_view release

[haleychaas]

Summary

This updates the documentation around the new agent_view and recommendations moving away from assistant_view, with links to the docs and changelog entry on that. I updated the code sample to match the sample app updates too.

Preview: https://docs-slack-d-branch-for-avumma.herokuapp.com/tools/bolt-python/concepts/adding-agent-features

Testing

Category

• 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

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

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.37%. Comparing base (3978707) to head (9b2ad00).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1543   +/-   ##
=======================================
  Coverage   91.37%   91.37%           
=======================================
  Files         228      228           
  Lines        7285     7285           
=======================================
  Hits         6657     6657           
  Misses        628      628           

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