### What changes were proposed in this pull request?
1. Replace the metadata key `org.apache.spark.int96NoRebase` by `org.apache.spark.legacyINT96`.
2. Change the condition when new key should be saved to parquet metadata: it should be saved when the SQL config `spark.sql.legacy.parquet.int96RebaseModeInWrite` is set to `LEGACY`.
3. Change handling the metadata key in read:
- If there is no the key in parquet metadata, take the rebase mode from the SQL config: `spark.sql.legacy.parquet.int96RebaseModeInRead`
- If parquet files were saved by Spark < 3.1.0, use the `LEGACY` rebasing mode for INT96 type.
- For files written by Spark >= 3.1.0, if the `org.apache.spark.legacyINT96` presents in metadata, perform rebasing otherwise don't.
### Why are the changes needed?
- To not increase parquet size by default when `spark.sql.legacy.parquet.int96RebaseModeInWrite` is `EXCEPTION` after https://github.com/apache/spark/pull/30121.
- To have the implementation similar to `org.apache.spark.legacyDateTime`
- To minimise impact on other subsystems that are based on file sizes like gathering statistics.
### Does this PR introduce _any_ user-facing change?
No
### How was this patch tested?
Modified test in `ParquetIOSuite`
Closes#30132 from MaxGekk/int96-flip-metadata-rebase-key.
Authored-by: Max Gekk <max.gekk@gmail.com>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>
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