Put DataFileMetadata::as_record_batch under #[internal_api]

[gotocoding-DB]

We use DataFileMetadata::as_record_batch to retry delta commits using the same uploaded parquet file (which is represented by DataFileMetadata).
Can we please mark it with internal_api?

What changes are proposed in this pull request?

How was this change tested?

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.65%. Comparing base (40bc46b) to head (f7b286b).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1409      +/-   ##
==========================================
- Coverage   84.65%   84.65%   -0.01%     
==========================================
  Files         115      115              
  Lines       29601    29597       -4     
  Branches    29601    29597       -4     
==========================================
- Hits        25059    25055       -4     
  Misses       3331     3331              
  Partials     1211     1211              

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[gotocoding-DB]

cc @zachschuermann @OussamaSaoudi to review