Add docs and examples for object_store_opendal

[Xuanwo]

object_store_opendal has been used by some users but we don't have a doc page for it. We need to improve this part.

related to: https://github.com/apache/arrow-rs/pull/5752#discussion_r1597420064

Tasks

• [ ] Add a README for this project, including
  • [ ] What's this project for
  • [ ] How to build/test/use this project
• Examples
  • [ ] Example for object_store
  • [ ] Example for datafusion
  • [ ] Example for polars
  • [ ] Example for delta-rs

[hanxuanliang]

This seems like a good opportunity to understand object_store, and I would like to give it a try.