docs: add Backblaze B2 to S3-compatible servers list

[goanpeca]

Adds Backblaze B2 to the list of named S3-compatible providers in the ## S3-compatible servers (non-Amazon) subsection, plus the bottom-of-section reference link. Same shape as how Nebius, MinIO, IBM Cloud Object Storage, and DigitalOcean Spaces are already mentioned — no new code blocks, no new example, just one more named provider.

The existing endpointurl example continues to use DigitalOcean. Credentials guidance lives in the ## Custom authentication section earlier on the same page and applies unchanged.

[CLAassistant]

All committers have signed the CLA.

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Updates the Amazon S3 remote storage documentation to mention Backblaze B2 as an S3-compatible option and adds the corresponding reference link.

Changes:

• Adds Backblaze B2 to the list of S3-compatible servers.
• Adds a Backblaze B2 markdown reference link.

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[goanpeca]

Matches the existing [digitalocean space] and [ibm cloud object storage] reference labels in the same file (lowercase, space-separated). Hyphenated form isn't used here.

[goanpeca]

Gentle ping @skshetry 🙂

Small docs-only change: adds Backblaze B2 to the S3-compatible providers list.

The only open thread is a Copilot label nitpick I've already replied to.

Thanks!