[object_store] Support MD5 checksum in attributes

[tzembo]

Which issue does this PR close?

Closes apache/arrow-rs-object-store#280

Rationale for this change

I would like AWS, Azure, and GCP to validate the data integrity of my uploaded objects. All three providers allow doing so by providing a Content-MD5 header with a 128-bit base64-encoded digest.

What changes are included in this PR?

See apache/arrow-rs-object-store#280

Are there any user-facing changes?

There's an additional Checksum attribute that can be set on requests.

[Jefffrey]

Looks like there are a few CI errors that'll need to be fixed

[alamb]

Marking as draft as I think this PR is no longer waiting on feedback. Please mark it as ready for review when it is ready for another look

[alamb]

Thank you for this PR. We are in the process of moving the object_store code to its own repository. Would it be possible for you to create a PR in that repository instead?

• See details on [EPIC] Port object_store content from arrow-rs repository arrow-rs-object-store#2
• Backstory on [DISCUSSION] Proposal move object_store to its own github repo? #6183

(we will handle moving all existing issues to the new repository)

[tzembo]

Absolutely - sorry for putting this up and then leaving it unattended, haven't had much bandwidth to get back to it recently. I will put something new together in the new repo 👍

[alamb]

Absolutely - sorry for putting this up and then leaving it unattended, haven't had much bandwidth to get back to it recently. I will put something new together in the new repo 👍

No worries !