docs: updates gif and enterprise paths

[lukegalbraithrussell]

Summary

We were linking to a github-hosted asset. That results in cookie shenanigans.

Grabbed the /enterprise-grid paths and changed them explicitly to their redirected /enterprise paths. The redirects were catching it, but it gives out warnings in our build anyway and that's annoying to me

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 90.98%. Comparing base (67b873d) to head (7bab511).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1358   +/-   ##
=======================================
  Coverage   90.98%   90.98%           
=======================================
  Files         222      222           
  Lines        7517     7517           
=======================================
  Hits         6839     6839           
  Misses        678      678           

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