[Python][Documentation] Document migration from ParquetDataset to pyarrow.datasets

[asfimport]

We need documentation describing a migration path from ParquetDataset, at least for the basic user facing API of ParquetDataset (As I read it, that's: construction, projection, filtering, threading, for a first pass). Following this we could mark ParquetDataset as deprecated, building features needed by power users like dask and adding those to the migration document

Reporter: Ben Kietzman / @bkietz

Related issues:

• [Python] Long-term fate of pyarrow.parquet.ParquetDataset (is related to)
• [Python] Add user guide documentation for Datasets API (is related to)

_{Note: This issue was originally created as ARROW-8047. Please see the migration documentation for further details.}

[asfimport]

Joris Van den Bossche / @jorisvandenbossche:
I also created ARROW-8063 for general user guide docs for the dataset module

[asfimport]

Krisztian Szucs / @kszucs:
You added examples in the guide, so I postpone it to the next release.

[asfimport]

Alessandro Molina / @amol-:
Postponing this to version 10

[asfimport]

Apache Arrow JIRA Bot:
This issue was last updated over 90 days ago, which may be an indication it is no longer being actively worked. To better reflect the current state, the issue is being unassigned per project policy. Please feel free to re-take assignment of the issue if it is being actively worked, or if you plan to start that work soon.

[github-actions]

This issue has been marked as stale because it has had no activity in the past 365 days. Please remove the stale label or comment below, or this issue will be closed in 14 days. If this improvement is still desired but has no current owner, please add the 'Status: needs champion' label.