Move URL signing to object_store crate

[tdikland]

In the discussion on apache/arrow-rs#22, @tustvold and @roeap pointed out the rust ecosystem is building abstractions over object stores (and consequently URL signing) in the object_store crate. Moving to object_store will simplify the implementation.

Dependencies

Before object_store can be integrated, it needs to support signing URLs for Azure and GCP. Alternatively we could also implement the Signer trait in this crate, but I think that would be wasteful.

• Azure Signed URL Support apache/arrow-rs-object-store#101
• GCS Signed URL Support apache/arrow-rs#5233

References:

object_store crate