chore: group docusaurus dependencies

[WilliamBergamin]

#1148 Failed with the following error message found in the CI pipeline

[cause]: Error: Invalid name=docusaurus-plugin-content-docs version number=3.5.2.
  All official @docusaurus/* packages should have the exact same version as @docusaurus/core (number=3.4.0).
  Maybe you want to check, or regenerate your yarn.lock or package-lock.json file?

This PR attempts to configure dependabot grouping for docusaurus dependencies. This should allow dependabot to update all docusaurus dependencies in one since PR preventing this type of breakage 🤔

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

All modified and coverable lines are covered by tests ✅

Project coverage is 92.02%. Comparing base (b3b05a9) to head (468c454).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1155   +/-   ##
=======================================
  Coverage   92.02%   92.02%           
=======================================
  Files         195      195           
  Lines        6631     6631           
=======================================
  Hits         6102     6102           
  Misses        529      529           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[filmaj]

Nice, didn't know you could do this!