Use "(none)" placeholder for default value of un-preset configs on confing doc page

[bowenliang123]

🔍 Description

Issue References 🔗

As descirbed.

Describe Your Solution 🔧

• Replace the placeholder for default value of un-preset configs on doc page, changed from <undefined> to (none)
• The (none) placeholder style is also used in the docs of
  • Spark : https://spark.apache.org/docs/latest/configuration.html
  • Flink : https://nightlies.apache.org/flink/flink-docs-master/docs/deployment/config/
  • Trino (as NONE): https://trino.io/docs/current/admin/properties.html
• Only affects the config doc page, no functional changes.

Types of changes 🔖

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Test Plan 🧪

Behavior Without This Pull Request ⚰️

No functional changes.

Config doc page:

Behavior With This Pull Request 🎉

No functional changes.

Config doc page:

Related Unit Tests

---

Checklists

📝 Author Self Checklist

• My code follows the style guidelines of this project
• I have performed a self-review
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• This patch was not authored or co-authored using Generative Tooling

📝 Committer Pre-Merge Checklist

• Pull request title is okay.
• No license issues.
• Milestone correctly set?
• Test coverage is ok
• Assignees are selected.
• Minimum number of approvals
• No changes are requested

Be nice. Be informative.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (c290dae) 61.57% compared to head (3b141dd) 61.54%.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #5916      +/-   ##
============================================
- Coverage     61.57%   61.54%   -0.03%     
  Complexity       23       23              
============================================
  Files           616      616              
  Lines         36386    36386              
  Branches       4978     4978              
============================================
- Hits          22404    22395       -9     
- Misses        11570    11572       +2     
- Partials       2412     2419       +7     

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[yaooqinn]

Only affects the config doc page, no functional changes

Could this be an unnotified breaking change, for example, the return value from retrieving an unset configuration?

BTW, (none) is only manually used on Spark's doc side. For its code side, it uses <undefined>

FYI, apache/spark#19974

[yaooqinn]

BTW, it seems that 📝 Committer Pre-Merge Checklist is not welcomed at all.

[bowenliang123]

Only affects the config doc page, no functional changes

Could this be an unnotified breaking change, for example, the return value from retrieving an unset configuration?

BTW, (none) is only manually used on Spark's doc side. For its code side, it uses <undefined>

FYI, apache/spark#19974

Let me think again. And if you have worries on this PR, feel free to revert it any time.

[yaooqinn]

If it's only related to doc change, I guess we can either optimize the CSS style or map to (none) in the test scope for doc generation. Let's revert it first as it might contain unexpected behaviors