split datafusion-object-store module

[yahoNanJing]

Which issue does this PR close?

Closes #1772.

Rationale for this change

By splitting the object store into a separate module, the object stores in datafusion-contrib no longer need to depend on the whole datafusion crate. They only need to depend on this separated module. What's more, if we hope to introduce the object stores in datafusion-contrib as some featuers in the datafusion crate, the issue of dependency cyclic can be avoided.

What changes are included in this PR?

• Introduces a new crate datafusion-storage for object store interfaces.
• Moves the object store in previous datasource mod into this new datafusion-storage crate.

The reason of still keeping ObjectStoreRegistry in the datafusion crate is

1. for future introduces object store features which can make it possible to have many default object stores besides the LocalFileSystem, like HadoopFileSystem in datafusion-objectstore-hdfs, S3FileSystem in datafusion-objectstore-s3.
2. the object stores in datafusion-contrib don't need it.

Are there any user-facing changes?

[yahoNanJing]

Hi @jimexist, @matthewmturner, @yjshen, @alamb, could you help review this patch?

[alamb]

Makes sense to me -- thank you @yahoNanJing

cc @yjshen @rdettai @matthewmturner and @tustvold

[matthewmturner]

Overall looks good. I think my only point, similar to what we discussed before, is on some of the ObjectStore functionality that is still hanging around in datafusion core i.e. ListingTable and functionality in datasource. I know the ObjectStore doesnt need them and this keeps datafusion-storage light, which of course is nice. To me they just seem logically coupled so at first was odd seeing the functionality split like that.

That being said, i have given this more thought and given how the above mentioned functionalities leverage physical plan, etc. i do think it makes sense to have datafusion wrap these functionalities together. just walking through my thought process out loud :)

thanks for this.

[alamb]

To me they just seem logically coupled so at first was odd seeing the functionality split like that.

🤔 maybe it is time for datafusion-listing-table crate

[liukun4515]

LGTM

[alamb]

🎉