feat: add gsutil_uri property on Blob

[KrazyAC]

Please review it if this request is acceptable. Thanks! @andrewsg

Pull Request

• Make sure to open an issue as a bug/issue before writing your code! That way we can discuss the change, evaluate designs, and agree on the general idea
• Ensure the tests and linter pass
• Code coverage does not decrease (if any source code was changed)
• Appropriate docs were updated (if necessary)

Fixes #896 🦕

[andrewsg]

Apologies for letting this sit for so long. When the PR was originally filed, we were beginning to work on support for universe domains internally, and that feature conflicted with this implementation. As non-default universe domains need to be supported going forward, I can't accept this PR as it is, but I will open a bug to track the work going forward and do my best to incorporate this idea into the final product. Thank you.