Add explanation caching nestjs docs

[junghyunbak]

Please check if the PR fulfills these requirements

• Followed the Contributing guidelines.
• Tests for the changes have been added (for bug fixes/features) with 100% code coverage.
• Docs have been added / updated (for bug fixes / features)

What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)

keyv - 'caching-nestjs' setup I would like to add a reference to the 'keyv' default prefix to the official manual.

Because I missed it and wandered in the migration from the cache-manager-ioredis library to keyv.

If the comments you added as an annotation are too long-winded, I hope that the annotation for namespace within KeyvRedisOptions type is revised.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (db5672e) to head (873dee8).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #1645   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           30        30           
  Lines         4087      4088    +1     
  Branches      1163      1165    +2     
=========================================
+ Hits          4087      4088    +1     

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[jaredwray]

@junghyunbak - thanks! This should go out in the next week or so