[WIP] Let guzzle choose the handler for http requests

[julien-nc]

So it can write a streamed response body progressively.

Summary

When using the 'stream' => true request option with IClient, the response body is a resource but its content is written all at once when the request is done.
This happens because the use of the CurlHandler is hardcoded in https://github.com/nextcloud/server/blob/fb67d5d/lib/private/Http/Client/ClientService.php#L44
The Curlhandler makes a blocking call to curl_exec which executes the request synchronously.

To allow progressive streamed responses, we need:

• to use HTTP 1/*
• to allow guzzle to use the StreamHandler

This is just a PoC. I have no idea if it's the right thing to do.
Wdyt?

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)

AI (if applicable)

• The content of this PR was partly or fully generated using AI