Doc: note enforce_batch_size_in_joins only applies to symmetric hash join

[2010YOUY01]

Which issue does this PR close?

• Closes #.

Rationale for this change

This config used to be applicable to most join operators

• Split output batches of joins that do not respect batch size #12969

Now only SHJ is using it, this PR updates the doc. (I think we can eventually deprecate it, but it requires further investigation, so it's left to future work, tracked in #24812)

To verify, search for the config name in the codebase, and only SHJ is using it.

What changes are included in this PR?

What is the testing strategy for this PR?

Are there any user-facing changes?

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.52%. Comparing base (e4cf35c) to head (b477e91).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #24811   +/-   ##
=======================================
  Coverage   81.52%   81.52%           
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  Files        1123     1123           
  Lines      406148   406230   +82     
  Branches   406148   406230   +82     
=======================================
+ Hits       331124   331191   +67     
- Misses      55659    55666    +7     
- Partials    19365    19373    +8     

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