docs: add runnable examples for input_file_name() and file_row_index()

[alamb]

Which issue does this PR close?

• N/A -- documentation only.

Rationale for this change

While writing a blog post

• Add DataFusion 55.0.0 release blog post datafusion-site#203

Which mentiones file_row_index() and input_file_name() -- I added a simple example for the post and I think it would help to have docs in the main site too.

What changes are included in this PR?

Replaces the sql_example with

> COPY (SELECT * from values (100), (200), (300)) to '/tmp/foo.parquet';

> select *, input_file_name(), file_row_index() from '/tmp/foo.parquet';
+---------+-------------------+------------------+
| column1 | input_file_name() | file_row_index() |
+---------+-------------------+------------------+
| 100     | tmp/foo.parquet   | 0                |
| 200     | tmp/foo.parquet   | 1                |
| 300     | tmp/foo.parquet   | 2                |
+---------+-------------------+------------------+

The same example is used for both functions, since showing them together is likely common and I think makes it clear what they do

Are these changes tested?

By CI

Are there any user-facing changes?

Yes, but documentation only -- the rendered examples for input_file_name()
and file_row_index() in the SQL function reference. No API or behavior
changes.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.43%. Comparing base (26b40dd) to head (cdc8928).

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #24634   +/-   ##
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  Coverage   81.43%   81.43%           
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  Files        1118     1118           
  Lines      399414   399414           
  Branches   399414   399414           
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  Hits       325278   325278           
+ Misses      55145    55141    -4     
- Partials    18991    18995    +4     

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[AdamGS]

LGTM 🙏