[Python] Mention alternatives in deprecation message of ParquetDataset attributes #29179

Follow-up on ARROW-13074.

We should maybe also expose the partitioning attribute on ParquetDataset (if constructed with use_legacy_dataset=False), as I did for the filesystem/files/fragments attributes.

Reporter: Joris Van den Bossche / @jorisvandenbossche
Assignee: Joris Van den Bossche / @jorisvandenbossche

Related issues:

• [Python] Start with deprecating ParquetDataset custom attributes (is related to)

PRs and other links:

• GitHub Pull Request #11380

_{Note: This issue was originally created as ARROW-13525. Please see the migration documentation for further details.}