feat: implement a walk function. (#24)

* feat: implement a `walk` function.

This commit implements a `walk` function that exposes the backends ability to
walk a cloud URL for objects prefixed by the given URL.

It can be used to glob a cloud storage URL.

* chore: update CHANGELOG.

* chore: bump dependencies.

* fix: treat the URL to `walk` as a directory.

* fix: handle trailing slash in URLs.

* fix: fix uploads for GCS backend.

* chore: update `Cargo.lock`.

Author: peterhuene

CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Unreleased
 
+#### Added
+
+* Implemented a `walk` function that can be used to glob a cloud storage URL ([#24](https://github.com/stjude-rust-labs/cloud-copy/pull/24)).
+
 #### Fixed
 
 * Improved progress bar message ([#23](https://github.com/stjude-rust-labs/cloud-copy/pull/23)).