[Python] Deprecate the (common_)metadata(_path) attributes of ParquetDataset #20181

The custom python ParquetDataset implementation exposes the metadata, metadata_path, common_metadata and common_metadata_path attributes, something for which we didn't add an equivalent to the new dataset API.

Unless we still want to add something for this, we should deprecate those attributes in the legacy ParquetDataset.

In addition, we should also deprecate passing the metadata keyword in the ParquetDataset constructor.

Reporter: Joris Van den Bossche / @jorisvandenbossche
Assignee: Alenka Frim / @AlenkaF

PRs and other links:

• GitHub Pull Request #12952

_{Note: This issue was originally created as ARROW-16121. Please see the migration documentation for further details.}